diff --git a/.changeset/refactor-pinia-colada-query.md b/.changeset/refactor-pinia-colada-query.md
new file mode 100644
index 0000000000..8e7d8c3b37
--- /dev/null
+++ b/.changeset/refactor-pinia-colada-query.md
@@ -0,0 +1,5 @@
+---
+"@hey-api/openapi-ts": patch
+---
+
+feat(pinia-colada): query options use `defineQueryOptions`
diff --git a/docs/data/people.ts b/docs/data/people.ts
index 662cb18a73..dc7e75b306 100644
--- a/docs/data/people.ts
+++ b/docs/data/people.ts
@@ -3,6 +3,11 @@ type Person = {
   name: string;
 };
 
+export const dmitriyBrolnickij: Person = {
+  github: 'https://github.com/brolnickij',
+  name: 'Dmitriy Brolnickij',
+};
+
 export const jacobCohen: Person = {
   github: 'https://github.com/jacobinu',
   name: 'Jacob Cohen',
diff --git a/docs/openapi-ts/clients/ofetch.md b/docs/openapi-ts/clients/ofetch.md
index 4798a0b1b0..14bb3ed01a 100644
--- a/docs/openapi-ts/clients/ofetch.md
+++ b/docs/openapi-ts/clients/ofetch.md
@@ -3,6 +3,11 @@ title: OFetch Client
 description: Generate a type-safe ofetch client from OpenAPI with the ofetch client for openapi-ts. Fully compatible with validators, transformers, and all core features.
 ---
 
+<script setup lang="ts">
+import AuthorsList from '@components/AuthorsList.vue';
+import { dmitriyBrolnickij } from '@data/people.js';
+</script>
+
 # OFetch
 
 ### About
@@ -11,6 +16,10 @@ description: Generate a type-safe ofetch client from OpenAPI with the ofetch cli
 
 The `ofetch` client for Hey API generates a type-safe client from your OpenAPI spec, fully compatible with validators, transformers, and all core features.
 
+### Collaborators
+
+<AuthorsList :people="[dmitriyBrolnickij]" />
+
 ## Features
 
 - seamless integration with `@hey-api/openapi-ts` ecosystem
diff --git a/docs/openapi-ts/plugins/pinia-colada.md b/docs/openapi-ts/plugins/pinia-colada.md
index 5ec2a00cc3..6c3c94cdb5 100644
--- a/docs/openapi-ts/plugins/pinia-colada.md
+++ b/docs/openapi-ts/plugins/pinia-colada.md
@@ -7,7 +7,7 @@ description: Generate Pinia Colada v0 functions and query keys from OpenAPI with
 import AuthorsList from '@components/AuthorsList.vue';
 import Heading from '@components/Heading.vue';
 import VersionLabel from '@components/VersionLabel.vue';
-import { joshHemphill, sebastiaanWouters } from '@data/people.js';
+import { joshHemphill, sebastiaanWouters, dmitriyBrolnickij } from '@data/people.js';
 </script>
 
 <Heading>
@@ -23,7 +23,7 @@ The Pinia Colada plugin for Hey API generates functions and query keys from your
 
 ### Collaborators
 
-<AuthorsList :people="[joshHemphill, sebastiaanWouters]" />
+<AuthorsList :people="[dmitriyBrolnickij, joshHemphill, sebastiaanWouters]" />
 
 ## Features
 
@@ -65,13 +65,11 @@ Queries are generated from [query operations](/openapi-ts/configuration/parser#h
 ::: code-group
 
 ```ts [example]
-const query = useQuery({
-  ...getPetByIdQuery({
-    path: {
-      petId: 1,
-    },
-  }),
-});
+const query = useQuery(getPetByIdQuery, () => ({
+  path: {
+    petId: 1,
+  },
+}));
 ```
 
 ```js [config]
diff --git a/examples/openapi-ts-pinia-colada/openapi-ts.config.ts b/examples/openapi-ts-pinia-colada/openapi-ts.config.ts
index 7a00915a40..a231ae4d61 100644
--- a/examples/openapi-ts-pinia-colada/openapi-ts.config.ts
+++ b/examples/openapi-ts-pinia-colada/openapi-ts.config.ts
@@ -18,7 +18,8 @@ export default defineConfig({
     },
     {
       exportFromIndex: true,
-      name: '@pinia/colada'
+      name: '@pinia/colada',
+      queryKeys: false
     }
   ]
 })
diff --git a/examples/openapi-ts-pinia-colada/src/client/@pinia/colada.gen.ts b/examples/openapi-ts-pinia-colada/src/client/@pinia/colada.gen.ts
index 21f0097478..1564abf607 100644
--- a/examples/openapi-ts-pinia-colada/src/client/@pinia/colada.gen.ts
+++ b/examples/openapi-ts-pinia-colada/src/client/@pinia/colada.gen.ts
@@ -1,5 +1,9 @@
 // This file is auto-generated by @hey-api/openapi-ts
 
+import { type _JSONValue, defineQueryOptions, type UseMutationOptions } from '@pinia/colada'
+
+import { client } from '../client.gen'
+import { serializeQueryKeyValue } from '../core/queryKeySerializer.gen'
 import {
   addPet,
   createUser,
@@ -24,8 +28,11 @@ import {
 } from '../sdk.gen'
 import type {
   AddPetData,
+  AddPetResponse,
   CreateUserData,
+  CreateUserResponse,
   CreateUsersWithListInputData,
+  CreateUsersWithListInputResponse,
   DeleteOrderData,
   DeletePetData,
   DeleteUserData,
@@ -38,19 +45,29 @@ import type {
   LoginUserData,
   LogoutUserData,
   PlaceOrderData,
+  PlaceOrderResponse,
   UpdatePetData,
+  UpdatePetResponse,
   UpdatePetWithFormData,
+  UpdatePetWithFormResponse,
   UpdateUserData,
-  UploadFileData
+  UploadFileData,
+  UploadFileResponse
 } from '../types.gen'
 
 /**
  * Add a new pet to the store.
  * Add a new pet to the store.
  */
-export const addPetMutation = () => ({
-  mutation: async (options: Options<AddPetData>) => {
-    const { data } = await addPet(options)
+export const addPetMutation = (
+  options?: Partial<Options<AddPetData>>
+): UseMutationOptions<AddPetResponse, Options<AddPetData>, Error> => ({
+  mutation: async (fnOptions) => {
+    const { data } = await addPet({
+      ...options,
+      ...fnOptions,
+      throwOnError: true
+    })
     return data
   }
 })
@@ -59,52 +76,106 @@ export const addPetMutation = () => ({
  * Update an existing pet.
  * Update an existing pet by Id.
  */
-export const updatePetMutation = () => ({
-  mutation: async (options: Options<UpdatePetData>) => {
-    const { data } = await updatePet(options)
+export const updatePetMutation = (
+  options?: Partial<Options<UpdatePetData>>
+): UseMutationOptions<UpdatePetResponse, Options<UpdatePetData>, Error> => ({
+  mutation: async (fnOptions) => {
+    const { data } = await updatePet({
+      ...options,
+      ...fnOptions,
+      throwOnError: true
+    })
     return data
   }
 })
 
+export type QueryKey<TOptions extends Options> = [
+  Pick<TOptions, 'baseUrl' | 'body' | 'path' | 'query'> & {
+    _id: string
+    baseUrl?: _JSONValue
+    body?: _JSONValue
+    query?: _JSONValue
+    tags?: _JSONValue
+  }
+]
+
+const createQueryKey = <TOptions extends Options>(
+  id: string,
+  options?: TOptions,
+  tags?: ReadonlyArray<string>
+): [QueryKey<TOptions>[0]] => {
+  const params: QueryKey<TOptions>[0] = {
+    _id: id,
+    baseUrl: options?.baseUrl || (options?.client ?? client).getConfig().baseUrl
+  } as QueryKey<TOptions>[0]
+  if (tags) {
+    params.tags = tags as unknown as _JSONValue
+  }
+  if (options?.body !== undefined) {
+    const normalizedBody = serializeQueryKeyValue(options.body)
+    if (normalizedBody !== undefined) {
+      params.body = normalizedBody
+    }
+  }
+  if (options?.path) {
+    params.path = options.path
+  }
+  if (options?.query !== undefined) {
+    const normalizedQuery = serializeQueryKeyValue(options.query)
+    if (normalizedQuery !== undefined) {
+      params.query = normalizedQuery
+    }
+  }
+  return [params]
+}
+
 /**
  * Finds Pets by status.
  * Multiple status values can be provided with comma separated strings.
  */
-export const findPetsByStatusQuery = (options: Options<FindPetsByStatusData>) => ({
-  key: ['findPetsByStatus', options?.path],
-  query: async (context: { signal: AbortSignal }) => {
-    const { data } = await findPetsByStatus({
-      ...options,
-      signal: context.signal,
-      throwOnError: true
-    })
-    return data
-  }
-})
+export const findPetsByStatusQuery = defineQueryOptions(
+  (options: Options<FindPetsByStatusData>) => ({
+    key: createQueryKey('findPetsByStatus', options),
+    query: async (context) => {
+      const { data } = await findPetsByStatus({
+        ...options,
+        ...context,
+        throwOnError: true
+      })
+      return data
+    }
+  })
+)
 
 /**
  * Finds Pets by tags.
  * Multiple tags can be provided with comma separated strings. Use tag1, tag2, tag3 for testing.
  */
-export const findPetsByTagsQuery = (options: Options<FindPetsByTagsData>) => ({
-  key: ['findPetsByTags', options?.path],
-  query: async (context: { signal: AbortSignal }) => {
+export const findPetsByTagsQuery = defineQueryOptions((options: Options<FindPetsByTagsData>) => ({
+  key: createQueryKey('findPetsByTags', options),
+  query: async (context) => {
     const { data } = await findPetsByTags({
       ...options,
-      signal: context.signal,
+      ...context,
       throwOnError: true
     })
     return data
   }
-})
+}))
 
 /**
  * Deletes a pet.
  * Delete a pet.
  */
-export const deletePetMutation = () => ({
-  mutation: async (options: Options<DeletePetData>) => {
-    const { data } = await deletePet(options)
+export const deletePetMutation = (
+  options?: Partial<Options<DeletePetData>>
+): UseMutationOptions<unknown, Options<DeletePetData>, Error> => ({
+  mutation: async (fnOptions) => {
+    const { data } = await deletePet({
+      ...options,
+      ...fnOptions,
+      throwOnError: true
+    })
     return data
   }
 })
@@ -113,25 +184,31 @@ export const deletePetMutation = () => ({
  * Find pet by ID.
  * Returns a single pet.
  */
-export const getPetByIdQuery = (options: Options<GetPetByIdData>) => ({
-  key: ['getPetById', options?.path],
-  query: async (context: { signal: AbortSignal }) => {
+export const getPetByIdQuery = defineQueryOptions((options: Options<GetPetByIdData>) => ({
+  key: createQueryKey('getPetById', options),
+  query: async (context) => {
     const { data } = await getPetById({
       ...options,
-      signal: context.signal,
+      ...context,
       throwOnError: true
     })
     return data
   }
-})
+}))
 
 /**
  * Updates a pet in the store with form data.
  * Updates a pet resource based on the form data.
  */
-export const updatePetWithFormMutation = () => ({
-  mutation: async (options: Options<UpdatePetWithFormData>) => {
-    const { data } = await updatePetWithForm(options)
+export const updatePetWithFormMutation = (
+  options?: Partial<Options<UpdatePetWithFormData>>
+): UseMutationOptions<UpdatePetWithFormResponse, Options<UpdatePetWithFormData>, Error> => ({
+  mutation: async (fnOptions) => {
+    const { data } = await updatePetWithForm({
+      ...options,
+      ...fnOptions,
+      throwOnError: true
+    })
     return data
   }
 })
@@ -140,9 +217,15 @@ export const updatePetWithFormMutation = () => ({
  * Uploads an image.
  * Upload image of the pet.
  */
-export const uploadFileMutation = () => ({
-  mutation: async (options: Options<UploadFileData>) => {
-    const { data } = await uploadFile(options)
+export const uploadFileMutation = (
+  options?: Partial<Options<UploadFileData>>
+): UseMutationOptions<UploadFileResponse, Options<UploadFileData>, Error> => ({
+  mutation: async (fnOptions) => {
+    const { data } = await uploadFile({
+      ...options,
+      ...fnOptions,
+      throwOnError: true
+    })
     return data
   }
 })
@@ -151,25 +234,31 @@ export const uploadFileMutation = () => ({
  * Returns pet inventories by status.
  * Returns a map of status codes to quantities.
  */
-export const getInventoryQuery = (options?: Options<GetInventoryData>) => ({
-  key: ['getInventory', options?.path],
-  query: async (context: { signal: AbortSignal }) => {
+export const getInventoryQuery = defineQueryOptions((options?: Options<GetInventoryData>) => ({
+  key: createQueryKey('getInventory', options),
+  query: async (context) => {
     const { data } = await getInventory({
       ...options,
-      signal: context.signal,
+      ...context,
       throwOnError: true
     })
     return data
   }
-})
+}))
 
 /**
  * Place an order for a pet.
  * Place a new order in the store.
  */
-export const placeOrderMutation = () => ({
-  mutation: async (options: Options<PlaceOrderData>) => {
-    const { data } = await placeOrder(options)
+export const placeOrderMutation = (
+  options?: Partial<Options<PlaceOrderData>>
+): UseMutationOptions<PlaceOrderResponse, Options<PlaceOrderData>, Error> => ({
+  mutation: async (fnOptions) => {
+    const { data } = await placeOrder({
+      ...options,
+      ...fnOptions,
+      throwOnError: true
+    })
     return data
   }
 })
@@ -178,9 +267,15 @@ export const placeOrderMutation = () => ({
  * Delete purchase order by identifier.
  * For valid response try integer IDs with value < 1000. Anything above 1000 or non-integers will generate API errors.
  */
-export const deleteOrderMutation = () => ({
-  mutation: async (options: Options<DeleteOrderData>) => {
-    const { data } = await deleteOrder(options)
+export const deleteOrderMutation = (
+  options?: Partial<Options<DeleteOrderData>>
+): UseMutationOptions<unknown, Options<DeleteOrderData>, Error> => ({
+  mutation: async (fnOptions) => {
+    const { data } = await deleteOrder({
+      ...options,
+      ...fnOptions,
+      throwOnError: true
+    })
     return data
   }
 })
@@ -189,25 +284,31 @@ export const deleteOrderMutation = () => ({
  * Find purchase order by ID.
  * For valid response try integer IDs with value <= 5 or > 10. Other values will generate exceptions.
  */
-export const getOrderByIdQuery = (options: Options<GetOrderByIdData>) => ({
-  key: ['getOrderById', options?.path],
-  query: async (context: { signal: AbortSignal }) => {
+export const getOrderByIdQuery = defineQueryOptions((options: Options<GetOrderByIdData>) => ({
+  key: createQueryKey('getOrderById', options),
+  query: async (context) => {
     const { data } = await getOrderById({
       ...options,
-      signal: context.signal,
+      ...context,
       throwOnError: true
     })
     return data
   }
-})
+}))
 
 /**
  * Create user.
  * This can only be done by the logged in user.
  */
-export const createUserMutation = () => ({
-  mutation: async (options: Options<CreateUserData>) => {
-    const { data } = await createUser(options)
+export const createUserMutation = (
+  options?: Partial<Options<CreateUserData>>
+): UseMutationOptions<CreateUserResponse, Options<CreateUserData>, Error> => ({
+  mutation: async (fnOptions) => {
+    const { data } = await createUser({
+      ...options,
+      ...fnOptions,
+      throwOnError: true
+    })
     return data
   }
 })
@@ -216,9 +317,19 @@ export const createUserMutation = () => ({
  * Creates list of users with given input array.
  * Creates list of users with given input array.
  */
-export const createUsersWithListInputMutation = () => ({
-  mutation: async (options: Options<CreateUsersWithListInputData>) => {
-    const { data } = await createUsersWithListInput(options)
+export const createUsersWithListInputMutation = (
+  options?: Partial<Options<CreateUsersWithListInputData>>
+): UseMutationOptions<
+  CreateUsersWithListInputResponse,
+  Options<CreateUsersWithListInputData>,
+  Error
+> => ({
+  mutation: async (fnOptions) => {
+    const { data } = await createUsersWithListInput({
+      ...options,
+      ...fnOptions,
+      throwOnError: true
+    })
     return data
   }
 })
@@ -227,41 +338,47 @@ export const createUsersWithListInputMutation = () => ({
  * Logs user into the system.
  * Log into the system.
  */
-export const loginUserQuery = (options?: Options<LoginUserData>) => ({
-  key: ['loginUser', options?.path],
-  query: async (context: { signal: AbortSignal }) => {
+export const loginUserQuery = defineQueryOptions((options?: Options<LoginUserData>) => ({
+  key: createQueryKey('loginUser', options),
+  query: async (context) => {
     const { data } = await loginUser({
       ...options,
-      signal: context.signal,
+      ...context,
       throwOnError: true
     })
     return data
   }
-})
+}))
 
 /**
  * Logs out current logged in user session.
  * Log user out of the system.
  */
-export const logoutUserQuery = (options?: Options<LogoutUserData>) => ({
-  key: ['logoutUser', options?.path],
-  query: async (context: { signal: AbortSignal }) => {
+export const logoutUserQuery = defineQueryOptions((options?: Options<LogoutUserData>) => ({
+  key: createQueryKey('logoutUser', options),
+  query: async (context) => {
     const { data } = await logoutUser({
       ...options,
-      signal: context.signal,
+      ...context,
       throwOnError: true
     })
     return data
   }
-})
+}))
 
 /**
  * Delete user resource.
  * This can only be done by the logged in user.
  */
-export const deleteUserMutation = () => ({
-  mutation: async (options: Options<DeleteUserData>) => {
-    const { data } = await deleteUser(options)
+export const deleteUserMutation = (
+  options?: Partial<Options<DeleteUserData>>
+): UseMutationOptions<unknown, Options<DeleteUserData>, Error> => ({
+  mutation: async (fnOptions) => {
+    const { data } = await deleteUser({
+      ...options,
+      ...fnOptions,
+      throwOnError: true
+    })
     return data
   }
 })
@@ -270,25 +387,31 @@ export const deleteUserMutation = () => ({
  * Get user by user name.
  * Get user detail based on username.
  */
-export const getUserByNameQuery = (options: Options<GetUserByNameData>) => ({
-  key: ['getUserByName', options?.path],
-  query: async (context: { signal: AbortSignal }) => {
+export const getUserByNameQuery = defineQueryOptions((options: Options<GetUserByNameData>) => ({
+  key: createQueryKey('getUserByName', options),
+  query: async (context) => {
     const { data } = await getUserByName({
       ...options,
-      signal: context.signal,
+      ...context,
       throwOnError: true
     })
     return data
   }
-})
+}))
 
 /**
  * Update user resource.
  * This can only be done by the logged in user.
  */
-export const updateUserMutation = () => ({
-  mutation: async (options: Options<UpdateUserData>) => {
-    const { data } = await updateUser(options)
+export const updateUserMutation = (
+  options?: Partial<Options<UpdateUserData>>
+): UseMutationOptions<unknown, Options<UpdateUserData>, Error> => ({
+  mutation: async (fnOptions) => {
+    const { data } = await updateUser({
+      ...options,
+      ...fnOptions,
+      throwOnError: true
+    })
     return data
   }
 })
diff --git a/examples/openapi-ts-pinia-colada/src/client/client.gen.ts b/examples/openapi-ts-pinia-colada/src/client/client.gen.ts
index 1984dc18c0..3431b130d4 100644
--- a/examples/openapi-ts-pinia-colada/src/client/client.gen.ts
+++ b/examples/openapi-ts-pinia-colada/src/client/client.gen.ts
@@ -1,12 +1,7 @@
 // This file is auto-generated by @hey-api/openapi-ts
 
-import {
-  type ClientOptions as DefaultClientOptions,
-  type Config,
-  createClient,
-  createConfig
-} from './client'
-import type { ClientOptions } from './types.gen'
+import { type ClientOptions, type Config, createClient, createConfig } from './client'
+import type { ClientOptions as ClientOptions2 } from './types.gen'
 
 /**
  * The `createClientConfig()` function will be called on client initialization
@@ -16,12 +11,12 @@ import type { ClientOptions } from './types.gen'
  * `setConfig()`. This is useful for example if you're using Next.js
  * to ensure your client always has the correct values.
  */
-export type CreateClientConfig<T extends DefaultClientOptions = ClientOptions> = (
-  override?: Config<DefaultClientOptions & T>
-) => Config<Required<DefaultClientOptions> & T>
+export type CreateClientConfig<T extends ClientOptions = ClientOptions2> = (
+  override?: Config<ClientOptions & T>
+) => Config<Required<ClientOptions> & T>
 
 export const client = createClient(
-  createConfig<ClientOptions>({
+  createConfig<ClientOptions2>({
     baseUrl: 'https://petstore3.swagger.io/api/v3'
   })
 )
diff --git a/examples/openapi-ts-pinia-colada/src/client/client/client.gen.ts b/examples/openapi-ts-pinia-colada/src/client/client/client.gen.ts
index 65910541f0..4a4fc4648f 100644
--- a/examples/openapi-ts-pinia-colada/src/client/client/client.gen.ts
+++ b/examples/openapi-ts-pinia-colada/src/client/client/client.gen.ts
@@ -2,6 +2,7 @@
 
 import { createSseClient } from '../core/serverSentEvents.gen'
 import type { HttpMethod } from '../core/types.gen'
+import { getValidRequestBody } from '../core/utils.gen'
 import type { Client, Config, RequestOptions, ResolvedRequestOptions } from './types.gen'
 import {
   buildUrl,
@@ -50,12 +51,12 @@ export const createClient = (config: Config = {}): Client => {
       await opts.requestValidator(opts)
     }
 
-    if (opts.body && opts.bodySerializer) {
+    if (opts.body !== undefined && opts.bodySerializer) {
       opts.serializedBody = opts.bodySerializer(opts.body)
     }
 
     // remove Content-Type header if body is empty to avoid sending invalid requests
-    if (opts.serializedBody === undefined || opts.serializedBody === '') {
+    if (opts.body === undefined || opts.serializedBody === '') {
       opts.headers.delete('Content-Type')
     }
 
@@ -70,12 +71,12 @@ export const createClient = (config: Config = {}): Client => {
     const requestInit: ReqInit = {
       redirect: 'follow',
       ...opts,
-      body: opts.serializedBody
+      body: getValidRequestBody(opts)
     }
 
     let request = new Request(url, requestInit)
 
-    for (const fn of interceptors.request._fns) {
+    for (const fn of interceptors.request.fns) {
       if (fn) {
         request = await fn(request, opts)
       }
@@ -86,7 +87,7 @@ export const createClient = (config: Config = {}): Client => {
     const _fetch = opts.fetch!
     let response = await _fetch(request)
 
-    for (const fn of interceptors.response._fns) {
+    for (const fn of interceptors.response.fns) {
       if (fn) {
         response = await fn(response, request, opts)
       }
@@ -98,20 +99,38 @@ export const createClient = (config: Config = {}): Client => {
     }
 
     if (response.ok) {
+      const parseAs =
+        (opts.parseAs === 'auto'
+          ? getParseAs(response.headers.get('Content-Type'))
+          : opts.parseAs) ?? 'json'
+
       if (response.status === 204 || response.headers.get('Content-Length') === '0') {
+        let emptyData: any
+        switch (parseAs) {
+          case 'arrayBuffer':
+          case 'blob':
+          case 'text':
+            emptyData = await response[parseAs]()
+            break
+          case 'formData':
+            emptyData = new FormData()
+            break
+          case 'stream':
+            emptyData = response.body
+            break
+          case 'json':
+          default:
+            emptyData = {}
+            break
+        }
         return opts.responseStyle === 'data'
-          ? {}
+          ? emptyData
           : {
-              data: {},
+              data: emptyData,
               ...result
             }
       }
 
-      const parseAs =
-        (opts.parseAs === 'auto'
-          ? getParseAs(response.headers.get('Content-Type'))
-          : opts.parseAs) ?? 'json'
-
       let data: any
       switch (parseAs) {
         case 'arrayBuffer':
@@ -160,7 +179,7 @@ export const createClient = (config: Config = {}): Client => {
     const error = jsonError ?? textError
     let finalError = error
 
-    for (const fn of interceptors.error._fns) {
+    for (const fn of interceptors.error.fns) {
       if (fn) {
         finalError = (await fn(error, response, request, opts)) as string
       }
@@ -191,6 +210,15 @@ export const createClient = (config: Config = {}): Client => {
       body: opts.body as BodyInit | null | undefined,
       headers: opts.headers as unknown as Record<string, string>,
       method,
+      onRequest: async (url, init) => {
+        let request = new Request(url, init)
+        for (const fn of interceptors.request.fns) {
+          if (fn) {
+            request = await fn(request, opts)
+          }
+        }
+        return request
+      },
       url
     })
   }
diff --git a/examples/openapi-ts-pinia-colada/src/client/client/types.gen.ts b/examples/openapi-ts-pinia-colada/src/client/client/types.gen.ts
index 273baf7860..b97f75e3fc 100644
--- a/examples/openapi-ts-pinia-colada/src/client/client/types.gen.ts
+++ b/examples/openapi-ts-pinia-colada/src/client/client/types.gen.ts
@@ -20,7 +20,7 @@ export interface Config<T extends ClientOptions = ClientOptions>
    *
    * @default globalThis.fetch
    */
-  fetch?: (request: Request) => ReturnType<typeof fetch>
+  fetch?: typeof fetch
   /**
    * Please don't use the Fetch client for Next.js applications. The `next`
    * options won't have any effect.
diff --git a/examples/openapi-ts-pinia-colada/src/client/client/utils.gen.ts b/examples/openapi-ts-pinia-colada/src/client/client/utils.gen.ts
index f701b3d78c..b42b5d9516 100644
--- a/examples/openapi-ts-pinia-colada/src/client/client/utils.gen.ts
+++ b/examples/openapi-ts-pinia-colada/src/client/client/utils.gen.ts
@@ -176,16 +176,24 @@ export const mergeConfigs = (a: Config, b: Config): Config => {
   return config
 }
 
+const headersEntries = (headers: Headers): Array<[string, string]> => {
+  const entries: Array<[string, string]> = []
+  headers.forEach((value, key) => {
+    entries.push([key, value])
+  })
+  return entries
+}
+
 export const mergeHeaders = (
   ...headers: Array<Required<Config>['headers'] | undefined>
 ): Headers => {
   const mergedHeaders = new Headers()
   for (const header of headers) {
-    if (!header || typeof header !== 'object') {
+    if (!header) {
       continue
     }
 
-    const iterator = header instanceof Headers ? header.entries() : Object.entries(header)
+    const iterator = header instanceof Headers ? headersEntries(header) : Object.entries(header)
 
     for (const [key, value] of iterator) {
       if (value === null) {
@@ -223,61 +231,58 @@ type ResInterceptor<Res, Req, Options> = (
 ) => Res | Promise<Res>
 
 class Interceptors<Interceptor> {
-  _fns: (Interceptor | null)[]
+  fns: Array<Interceptor | null> = []
 
-  constructor() {
-    this._fns = []
+  clear(): void {
+    this.fns = []
   }
 
-  clear() {
-    this._fns = []
-  }
-
-  getInterceptorIndex(id: number | Interceptor): number {
-    if (typeof id === 'number') {
-      return this._fns[id] ? id : -1
-    } else {
-      return this._fns.indexOf(id)
+  eject(id: number | Interceptor): void {
+    const index = this.getInterceptorIndex(id)
+    if (this.fns[index]) {
+      this.fns[index] = null
     }
   }
-  exists(id: number | Interceptor) {
+
+  exists(id: number | Interceptor): boolean {
     const index = this.getInterceptorIndex(id)
-    return !!this._fns[index]
+    return Boolean(this.fns[index])
   }
 
-  eject(id: number | Interceptor) {
-    const index = this.getInterceptorIndex(id)
-    if (this._fns[index]) {
-      this._fns[index] = null
+  getInterceptorIndex(id: number | Interceptor): number {
+    if (typeof id === 'number') {
+      return this.fns[id] ? id : -1
     }
+    return this.fns.indexOf(id)
   }
 
-  update(id: number | Interceptor, fn: Interceptor) {
+  update(id: number | Interceptor, fn: Interceptor): number | Interceptor | false {
     const index = this.getInterceptorIndex(id)
-    if (this._fns[index]) {
-      this._fns[index] = fn
+    if (this.fns[index]) {
+      this.fns[index] = fn
       return id
-    } else {
-      return false
     }
+    return false
   }
 
-  use(fn: Interceptor) {
-    this._fns = [...this._fns, fn]
-    return this._fns.length - 1
+  use(fn: Interceptor): number {
+    this.fns.push(fn)
+    return this.fns.length - 1
   }
 }
 
-// `createInterceptors()` response, meant for external use as it does not
-// expose internals
 export interface Middleware<Req, Res, Err, Options> {
-  error: Pick<Interceptors<ErrInterceptor<Err, Res, Req, Options>>, 'eject' | 'use'>
-  request: Pick<Interceptors<ReqInterceptor<Req, Options>>, 'eject' | 'use'>
-  response: Pick<Interceptors<ResInterceptor<Res, Req, Options>>, 'eject' | 'use'>
+  error: Interceptors<ErrInterceptor<Err, Res, Req, Options>>
+  request: Interceptors<ReqInterceptor<Req, Options>>
+  response: Interceptors<ResInterceptor<Res, Req, Options>>
 }
 
-// do not add `Middleware` as return type so we can use _fns internally
-export const createInterceptors = <Req, Res, Err, Options>() => ({
+export const createInterceptors = <Req, Res, Err, Options>(): Middleware<
+  Req,
+  Res,
+  Err,
+  Options
+> => ({
   error: new Interceptors<ErrInterceptor<Err, Res, Req, Options>>(),
   request: new Interceptors<ReqInterceptor<Req, Options>>(),
   response: new Interceptors<ResInterceptor<Res, Req, Options>>()
diff --git a/examples/openapi-ts-pinia-colada/src/client/core/queryKeySerializer.gen.ts b/examples/openapi-ts-pinia-colada/src/client/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..7e9d0d1ec8
--- /dev/null
+++ b/examples/openapi-ts-pinia-colada/src/client/core/queryKeySerializer.gen.ts
@@ -0,0 +1,117 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue }
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (value === undefined || typeof value === 'function' || typeof value === 'symbol') {
+    return undefined
+  }
+  if (typeof value === 'bigint') {
+    return value.toString()
+  }
+  if (value instanceof Date) {
+    return value.toISOString()
+  }
+  return value
+}
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer)
+    if (json === undefined) {
+      return undefined
+    }
+    return JSON.parse(json) as JsonValue
+  } catch {
+    return undefined
+  }
+}
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false
+  }
+  const prototype = Object.getPrototypeOf(value as object)
+  return prototype === Object.prototype || prototype === null
+}
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) => a.localeCompare(b))
+  const result: Record<string, JsonValue> = {}
+
+  for (const [key, value] of entries) {
+    const existing = result[key]
+    if (existing === undefined) {
+      result[key] = value
+      continue
+    }
+
+    if (Array.isArray(existing)) {
+      ;(existing as string[]).push(value)
+    } else {
+      result[key] = [existing, value]
+    }
+  }
+
+  return result
+}
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (value: unknown): JsonValue | undefined => {
+  if (value === null) {
+    return null
+  }
+
+  if (typeof value === 'string' || typeof value === 'number' || typeof value === 'boolean') {
+    return value
+  }
+
+  if (value === undefined || typeof value === 'function' || typeof value === 'symbol') {
+    return undefined
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString()
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString()
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value)
+  }
+
+  if (typeof URLSearchParams !== 'undefined' && value instanceof URLSearchParams) {
+    return serializeSearchParams(value)
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value)
+  }
+
+  return undefined
+}
diff --git a/examples/openapi-ts-pinia-colada/src/client/core/serverSentEvents.gen.ts b/examples/openapi-ts-pinia-colada/src/client/core/serverSentEvents.gen.ts
index de07ebaf27..372e50cc26 100644
--- a/examples/openapi-ts-pinia-colada/src/client/core/serverSentEvents.gen.ts
+++ b/examples/openapi-ts-pinia-colada/src/client/core/serverSentEvents.gen.ts
@@ -4,6 +4,17 @@ import type { Config } from './types.gen'
 
 export type ServerSentEventsOptions<TData = unknown> = Omit<RequestInit, 'method'> &
   Pick<Config, 'method' | 'responseTransformer' | 'responseValidator'> & {
+    /**
+     * Fetch API implementation. You can use this option to provide a custom
+     * fetch instance.
+     *
+     * @default globalThis.fetch
+     */
+    fetch?: typeof fetch
+    /**
+     * Implementing clients can call request interceptors inside this hook.
+     */
+    onRequest?: (url: string, init: RequestInit) => Promise<Request>
     /**
      * Callback invoked when a network or parsing error occurs during streaming.
      *
@@ -21,6 +32,7 @@ export type ServerSentEventsOptions<TData = unknown> = Omit<RequestInit, 'method
      * @returns Nothing (void).
      */
     onSseEvent?: (event: StreamEvent<TData>) => void
+    serializedBody?: RequestInit['body']
     /**
      * Default retry delay in milliseconds.
      *
@@ -68,6 +80,7 @@ export type ServerSentEventsResult<TData = unknown, TReturn = void, TNext = unkn
 }
 
 export const createSseClient = <TData = unknown>({
+  onRequest,
   onSseError,
   onSseEvent,
   responseTransformer,
@@ -103,7 +116,21 @@ export const createSseClient = <TData = unknown>({
       }
 
       try {
-        const response = await fetch(url, { ...options, headers, signal })
+        const requestInit: RequestInit = {
+          redirect: 'follow',
+          ...options,
+          body: options.serializedBody,
+          headers,
+          signal
+        }
+        let request = new Request(url, requestInit)
+        if (onRequest) {
+          request = await onRequest(url, requestInit)
+        }
+        // fetch must be assigned here, otherwise it would throw the error:
+        // TypeError: Failed to execute 'fetch' on 'Window': Illegal invocation
+        const _fetch = options.fetch ?? globalThis.fetch
+        const response = await _fetch(request)
 
         if (!response.ok) throw new Error(`SSE failed: ${response.status} ${response.statusText}`)
 
diff --git a/examples/openapi-ts-pinia-colada/src/client/core/utils.gen.ts b/examples/openapi-ts-pinia-colada/src/client/core/utils.gen.ts
index b99c527aac..bd078be240 100644
--- a/examples/openapi-ts-pinia-colada/src/client/core/utils.gen.ts
+++ b/examples/openapi-ts-pinia-colada/src/client/core/utils.gen.ts
@@ -1,6 +1,6 @@
 // This file is auto-generated by @hey-api/openapi-ts
 
-import type { QuerySerializer } from './bodySerializer.gen'
+import type { BodySerializer, QuerySerializer } from './bodySerializer.gen'
 import {
   type ArraySeparatorStyle,
   serializeArrayParam,
@@ -109,3 +109,32 @@ export const getUrl = ({
   }
   return url
 }
+
+export function getValidRequestBody(options: {
+  body?: unknown
+  bodySerializer?: BodySerializer | null
+  serializedBody?: unknown
+}) {
+  const hasBody = options.body !== undefined
+  const isSerializedBody = hasBody && options.bodySerializer
+
+  if (isSerializedBody) {
+    if ('serializedBody' in options) {
+      const hasSerializedBody =
+        options.serializedBody !== undefined && options.serializedBody !== ''
+
+      return hasSerializedBody ? options.serializedBody : null
+    }
+
+    // not all clients implement a serializedBody property (i.e. client-axios)
+    return options.body !== '' ? options.body : null
+  }
+
+  // plain/text body
+  if (hasBody) {
+    return options.body
+  }
+
+  // no body was provided
+  return undefined
+}
diff --git a/examples/openapi-ts-pinia-colada/src/client/index.ts b/examples/openapi-ts-pinia-colada/src/client/index.ts
index 2543e57505..b190962d22 100644
--- a/examples/openapi-ts-pinia-colada/src/client/index.ts
+++ b/examples/openapi-ts-pinia-colada/src/client/index.ts
@@ -1,4 +1,5 @@
 // This file is auto-generated by @hey-api/openapi-ts
+
 export * from './@pinia/colada.gen'
 export * from './sdk.gen'
-export * from './types.gen'
+export type * from './types.gen'
diff --git a/examples/openapi-ts-pinia-colada/src/client/sdk.gen.ts b/examples/openapi-ts-pinia-colada/src/client/sdk.gen.ts
index f373c7cf6f..37778ac7f8 100644
--- a/examples/openapi-ts-pinia-colada/src/client/sdk.gen.ts
+++ b/examples/openapi-ts-pinia-colada/src/client/sdk.gen.ts
@@ -1,7 +1,7 @@
 // This file is auto-generated by @hey-api/openapi-ts
 
-import type { Client, Options as ClientOptions, TDataShape } from './client'
-import { client as _heyApiClient } from './client.gen'
+import type { Client, Options as Options2, TDataShape } from './client'
+import { client } from './client.gen'
 import type {
   AddPetData,
   AddPetErrors,
@@ -65,7 +65,7 @@ import type {
 export type Options<
   TData extends TDataShape = TDataShape,
   ThrowOnError extends boolean = boolean
-> = ClientOptions<TData, ThrowOnError> & {
+> = Options2<TData, ThrowOnError> & {
   /**
    * You can provide a client instance returned by `createClient()` instead of
    * individual options. This might be also useful if you want to implement a
@@ -86,7 +86,7 @@ export type Options<
 export const addPet = <ThrowOnError extends boolean = false>(
   options: Options<AddPetData, ThrowOnError>
 ) =>
-  (options.client ?? _heyApiClient).post<AddPetResponses, AddPetErrors, ThrowOnError>({
+  (options.client ?? client).post<AddPetResponses, AddPetErrors, ThrowOnError>({
     security: [
       {
         scheme: 'bearer',
@@ -108,7 +108,7 @@ export const addPet = <ThrowOnError extends boolean = false>(
 export const updatePet = <ThrowOnError extends boolean = false>(
   options: Options<UpdatePetData, ThrowOnError>
 ) =>
-  (options.client ?? _heyApiClient).put<UpdatePetResponses, UpdatePetErrors, ThrowOnError>({
+  (options.client ?? client).put<UpdatePetResponses, UpdatePetErrors, ThrowOnError>({
     security: [
       {
         scheme: 'bearer',
@@ -130,11 +130,7 @@ export const updatePet = <ThrowOnError extends boolean = false>(
 export const findPetsByStatus = <ThrowOnError extends boolean = false>(
   options: Options<FindPetsByStatusData, ThrowOnError>
 ) =>
-  (options.client ?? _heyApiClient).get<
-    FindPetsByStatusResponses,
-    FindPetsByStatusErrors,
-    ThrowOnError
-  >({
+  (options.client ?? client).get<FindPetsByStatusResponses, FindPetsByStatusErrors, ThrowOnError>({
     security: [
       {
         scheme: 'bearer',
@@ -152,11 +148,7 @@ export const findPetsByStatus = <ThrowOnError extends boolean = false>(
 export const findPetsByTags = <ThrowOnError extends boolean = false>(
   options: Options<FindPetsByTagsData, ThrowOnError>
 ) =>
-  (options.client ?? _heyApiClient).get<
-    FindPetsByTagsResponses,
-    FindPetsByTagsErrors,
-    ThrowOnError
-  >({
+  (options.client ?? client).get<FindPetsByTagsResponses, FindPetsByTagsErrors, ThrowOnError>({
     security: [
       {
         scheme: 'bearer',
@@ -174,7 +166,7 @@ export const findPetsByTags = <ThrowOnError extends boolean = false>(
 export const deletePet = <ThrowOnError extends boolean = false>(
   options: Options<DeletePetData, ThrowOnError>
 ) =>
-  (options.client ?? _heyApiClient).delete<DeletePetResponses, DeletePetErrors, ThrowOnError>({
+  (options.client ?? client).delete<DeletePetResponses, DeletePetErrors, ThrowOnError>({
     security: [
       {
         scheme: 'bearer',
@@ -192,7 +184,7 @@ export const deletePet = <ThrowOnError extends boolean = false>(
 export const getPetById = <ThrowOnError extends boolean = false>(
   options: Options<GetPetByIdData, ThrowOnError>
 ) =>
-  (options.client ?? _heyApiClient).get<GetPetByIdResponses, GetPetByIdErrors, ThrowOnError>({
+  (options.client ?? client).get<GetPetByIdResponses, GetPetByIdErrors, ThrowOnError>({
     security: [
       {
         name: 'api_key',
@@ -214,7 +206,7 @@ export const getPetById = <ThrowOnError extends boolean = false>(
 export const updatePetWithForm = <ThrowOnError extends boolean = false>(
   options: Options<UpdatePetWithFormData, ThrowOnError>
 ) =>
-  (options.client ?? _heyApiClient).post<
+  (options.client ?? client).post<
     UpdatePetWithFormResponses,
     UpdatePetWithFormErrors,
     ThrowOnError
@@ -236,7 +228,7 @@ export const updatePetWithForm = <ThrowOnError extends boolean = false>(
 export const uploadFile = <ThrowOnError extends boolean = false>(
   options: Options<UploadFileData, ThrowOnError>
 ) =>
-  (options.client ?? _heyApiClient).post<UploadFileResponses, UploadFileErrors, ThrowOnError>({
+  (options.client ?? client).post<UploadFileResponses, UploadFileErrors, ThrowOnError>({
     bodySerializer: null,
     security: [
       {
@@ -259,7 +251,7 @@ export const uploadFile = <ThrowOnError extends boolean = false>(
 export const getInventory = <ThrowOnError extends boolean = false>(
   options?: Options<GetInventoryData, ThrowOnError>
 ) =>
-  (options?.client ?? _heyApiClient).get<GetInventoryResponses, GetInventoryErrors, ThrowOnError>({
+  (options?.client ?? client).get<GetInventoryResponses, GetInventoryErrors, ThrowOnError>({
     security: [
       {
         name: 'api_key',
@@ -277,7 +269,7 @@ export const getInventory = <ThrowOnError extends boolean = false>(
 export const placeOrder = <ThrowOnError extends boolean = false>(
   options?: Options<PlaceOrderData, ThrowOnError>
 ) =>
-  (options?.client ?? _heyApiClient).post<PlaceOrderResponses, PlaceOrderErrors, ThrowOnError>({
+  (options?.client ?? client).post<PlaceOrderResponses, PlaceOrderErrors, ThrowOnError>({
     url: '/store/order',
     ...options,
     headers: {
@@ -293,7 +285,7 @@ export const placeOrder = <ThrowOnError extends boolean = false>(
 export const deleteOrder = <ThrowOnError extends boolean = false>(
   options: Options<DeleteOrderData, ThrowOnError>
 ) =>
-  (options.client ?? _heyApiClient).delete<DeleteOrderResponses, DeleteOrderErrors, ThrowOnError>({
+  (options.client ?? client).delete<DeleteOrderResponses, DeleteOrderErrors, ThrowOnError>({
     url: '/store/order/{orderId}',
     ...options
   })
@@ -305,7 +297,7 @@ export const deleteOrder = <ThrowOnError extends boolean = false>(
 export const getOrderById = <ThrowOnError extends boolean = false>(
   options: Options<GetOrderByIdData, ThrowOnError>
 ) =>
-  (options.client ?? _heyApiClient).get<GetOrderByIdResponses, GetOrderByIdErrors, ThrowOnError>({
+  (options.client ?? client).get<GetOrderByIdResponses, GetOrderByIdErrors, ThrowOnError>({
     url: '/store/order/{orderId}',
     ...options
   })
@@ -317,7 +309,7 @@ export const getOrderById = <ThrowOnError extends boolean = false>(
 export const createUser = <ThrowOnError extends boolean = false>(
   options?: Options<CreateUserData, ThrowOnError>
 ) =>
-  (options?.client ?? _heyApiClient).post<CreateUserResponses, CreateUserErrors, ThrowOnError>({
+  (options?.client ?? client).post<CreateUserResponses, CreateUserErrors, ThrowOnError>({
     url: '/user',
     ...options,
     headers: {
@@ -333,7 +325,7 @@ export const createUser = <ThrowOnError extends boolean = false>(
 export const createUsersWithListInput = <ThrowOnError extends boolean = false>(
   options?: Options<CreateUsersWithListInputData, ThrowOnError>
 ) =>
-  (options?.client ?? _heyApiClient).post<
+  (options?.client ?? client).post<
     CreateUsersWithListInputResponses,
     CreateUsersWithListInputErrors,
     ThrowOnError
@@ -353,7 +345,7 @@ export const createUsersWithListInput = <ThrowOnError extends boolean = false>(
 export const loginUser = <ThrowOnError extends boolean = false>(
   options?: Options<LoginUserData, ThrowOnError>
 ) =>
-  (options?.client ?? _heyApiClient).get<LoginUserResponses, LoginUserErrors, ThrowOnError>({
+  (options?.client ?? client).get<LoginUserResponses, LoginUserErrors, ThrowOnError>({
     url: '/user/login',
     ...options
   })
@@ -365,7 +357,7 @@ export const loginUser = <ThrowOnError extends boolean = false>(
 export const logoutUser = <ThrowOnError extends boolean = false>(
   options?: Options<LogoutUserData, ThrowOnError>
 ) =>
-  (options?.client ?? _heyApiClient).get<LogoutUserResponses, LogoutUserErrors, ThrowOnError>({
+  (options?.client ?? client).get<LogoutUserResponses, LogoutUserErrors, ThrowOnError>({
     url: '/user/logout',
     ...options
   })
@@ -377,7 +369,7 @@ export const logoutUser = <ThrowOnError extends boolean = false>(
 export const deleteUser = <ThrowOnError extends boolean = false>(
   options: Options<DeleteUserData, ThrowOnError>
 ) =>
-  (options.client ?? _heyApiClient).delete<DeleteUserResponses, DeleteUserErrors, ThrowOnError>({
+  (options.client ?? client).delete<DeleteUserResponses, DeleteUserErrors, ThrowOnError>({
     url: '/user/{username}',
     ...options
   })
@@ -389,7 +381,7 @@ export const deleteUser = <ThrowOnError extends boolean = false>(
 export const getUserByName = <ThrowOnError extends boolean = false>(
   options: Options<GetUserByNameData, ThrowOnError>
 ) =>
-  (options.client ?? _heyApiClient).get<GetUserByNameResponses, GetUserByNameErrors, ThrowOnError>({
+  (options.client ?? client).get<GetUserByNameResponses, GetUserByNameErrors, ThrowOnError>({
     url: '/user/{username}',
     ...options
   })
@@ -401,7 +393,7 @@ export const getUserByName = <ThrowOnError extends boolean = false>(
 export const updateUser = <ThrowOnError extends boolean = false>(
   options: Options<UpdateUserData, ThrowOnError>
 ) =>
-  (options.client ?? _heyApiClient).put<UpdateUserResponses, UpdateUserErrors, ThrowOnError>({
+  (options.client ?? client).put<UpdateUserResponses, UpdateUserErrors, ThrowOnError>({
     url: '/user/{username}',
     ...options,
     headers: {
diff --git a/examples/openapi-ts-pinia-colada/src/client/types.gen.ts b/examples/openapi-ts-pinia-colada/src/client/types.gen.ts
index f7044e662a..99ce8e7d8e 100644
--- a/examples/openapi-ts-pinia-colada/src/client/types.gen.ts
+++ b/examples/openapi-ts-pinia-colada/src/client/types.gen.ts
@@ -1,5 +1,9 @@
 // This file is auto-generated by @hey-api/openapi-ts
 
+export type ClientOptions = {
+  baseUrl: 'https://petstore3.swagger.io/api/v3' | (string & {})
+}
+
 export type Order = {
   complete?: boolean
   id?: number
@@ -687,7 +691,3 @@ export type UpdateUserResponses = {
    */
   200: unknown
 }
-
-export type ClientOptions = {
-  baseUrl: 'https://petstore3.swagger.io/api/v3' | (string & {})
-}
diff --git a/examples/openapi-ts-pinia-colada/src/views/PiniaColadaExample.vue b/examples/openapi-ts-pinia-colada/src/views/PiniaColadaExample.vue
index 6930fc78a2..a0e5557da4 100644
--- a/examples/openapi-ts-pinia-colada/src/views/PiniaColadaExample.vue
+++ b/examples/openapi-ts-pinia-colada/src/views/PiniaColadaExample.vue
@@ -1,11 +1,12 @@
 <script lang="ts" setup>
 import type { Pet } from '@/client'
+import type { RequestOptions } from '@/client/client'
+import { PiniaColadaDevtools } from '@pinia/colada-devtools'
 import { createClient } from '@/client/client'
 import { PetSchema } from '@/client/schemas.gen'
 import { addPetMutation, getPetByIdQuery, updatePetMutation } from '@/client/@pinia/colada.gen'
-import { useQuery, useMutation } from '@pinia/colada'
+import { useQuery, useMutation, useQueryCache } from '@pinia/colada'
 import { ref, watch } from 'vue'
-import type { RequestOptions } from '@/client/client'
 
 const localClient = createClient({
   // set default base url for requests made by this client
@@ -30,106 +31,94 @@ localClient.interceptors.request.use((request: Request, options: RequestOptions)
   return request
 })
 
-const pet = ref<Pet>()
-const petId = ref<number>()
+const isPetNameRequired = PetSchema.required.includes('name')
 
+const petId = ref<number | undefined>()
 const petInput = ref({ name: '', category: '' })
 
-const addPet = useMutation(addPetMutation())
-
-const updatePet = useMutation(updatePetMutation())
-
-const { data, error } = useQuery(() => {
-  if (!petId.value) {
-    return {
-      key: ['getPetById', 'none'],
-      query: async () => undefined,
-      enabled: false
+const { data: pet, error } = useQuery(() => ({
+  ...getPetByIdQuery({
+    path: {
+      petId: petId.value as number
     }
-  }
+  }),
+  enabled: petId.value !== undefined
+}))
+const { mutateAsync: createPet } = useMutation(addPetMutation())
+const { mutateAsync: updatePet } = useMutation(updatePetMutation())
+
+const queryCache = useQueryCache()
+async function invalidateCurrentPet() {
+  const { key } = getPetByIdQuery({
+    path: {
+      petId: petId.value as number
+    }
+  })
+  await queryCache.invalidateQueries({ key, exact: true })
+}
 
-  return {
-    ...getPetByIdQuery({
-      client: localClient,
-      path: {
-        petId: petId.value
-      }
-    }),
-    enabled: true
+async function updatePetIdAndInvalidate(newId: number | undefined) {
+  if (newId !== undefined) {
+    petId.value = newId
   }
-})
 
-const handleAddPet = async () => {
-  if (PetSchema.required.includes('name') && !petInput.value?.name?.length) {
-    return
+  if (petId.value !== undefined) {
+    await invalidateCurrentPet()
   }
+}
 
-  const result = await addPet.mutateAsync({
-    body: {
-      category: {
-        id: 0,
-        name: petInput.value.category
-      },
-      id: 0,
-      name: petInput.value?.name,
-      photoUrls: ['string'],
-      status: 'available',
-      tags: [
-        {
-          id: 0,
-          name: 'string'
-        }
-      ]
-    }
-  })
+async function handleAddPet() {
+  if (isPetNameRequired && !petInput.value.name) return
 
-  if (result) {
-    pet.value = result
-    petId.value = result.id ?? petId.value
-  }
-}
+  const result = await createPet({ body: buildPetBody() })
+  if (!result) return
 
-function setRandomPetId() {
-  // random id 1-10
-  petId.value = Math.floor(Math.random() * (10 - 1 + 1) + 1)
+  await updatePetIdAndInvalidate(result.id)
 }
 
-const handleUpdatePet = async () => {
-  const result = await updatePet.mutateAsync({
-    body: {
-      category: {
-        id: pet.value?.category?.id ?? 0,
-        name: petInput.value.category
-      },
-      id: pet.value?.id ?? 0,
-      name: petInput.value.name,
-      photoUrls: ['string'],
-      status: 'available',
-      tags: [
-        {
-          id: 0,
-          name: 'string'
-        }
-      ]
-    },
-    // setting headers per request
+async function handleUpdatePet() {
+  if (!pet.value) return
+
+  const result = await updatePet({
+    body: buildPetBody(pet.value),
     headers: {
       Authorization: 'Bearer <token_from_method>'
     }
   })
+  if (!result) return
 
-  if (result) {
-    pet.value = result
-    petId.value = result.id ?? petId.value
-  }
+  await updatePetIdAndInvalidate(result.id)
 }
 
-watch(data, () => {
-  pet.value = data.value as Pet | undefined
-})
+function randomInt(min: number, max: number) {
+  return Math.floor(Math.random() * (max - min + 1) + min)
+}
+
+function setRandomPetId() {
+  petId.value = randomInt(1, 10)
+}
+
+function buildPetBody(base?: Partial<Pet>) {
+  return {
+    category: {
+      id: base?.category?.id ?? 0,
+      name: petInput.value.category
+    },
+    id: base?.id ?? 0,
+    name: petInput.value.name,
+    photoUrls: ['string'],
+    status: 'available' as const,
+    tags: [
+      {
+        id: 0,
+        name: 'string'
+      }
+    ]
+  }
+}
 
 watch(error, (error) => {
-  console.log(error)
+  console.error(error)
 })
 </script>
 
@@ -218,4 +207,6 @@ watch(error, (error) => {
       </form>
     </div>
   </div>
+
+  <pinia-colada-devtools />
 </template>
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/body-response-text-plain/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/body-response-text-plain/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/body-response-text-plain/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/body-response-text-plain/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/body-response-text-plain/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/body-response-text-plain/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/body-response-text-plain/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/form-data/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/form-data/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/form-data/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/form-data/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/form-data/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/form-data/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/form-data/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@angular/common/default-class/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@angular/common/default-class/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@angular/common/default-class/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@angular/common/default-class/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@angular/common/default-class/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@angular/common/default-class/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@angular/common/default-class/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@angular/common/default/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@angular/common/default/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@angular/common/default/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@angular/common/default/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@angular/common/default/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@angular/common/default/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@angular/common/default/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/client-fetch/sdk-nested-classes-instance/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/client-fetch/sdk-nested-classes-instance/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/client-fetch/sdk-nested-classes-instance/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/client-fetch/sdk-nested-classes-instance/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/client-fetch/sdk-nested-classes-instance/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/client-fetch/sdk-nested-classes-instance/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/client-fetch/sdk-nested-classes-instance/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/client-fetch/sdk-nested-classes/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/client-fetch/sdk-nested-classes/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/client-fetch/sdk-nested-classes/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/client-fetch/sdk-nested-classes/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/client-fetch/sdk-nested-classes/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/client-fetch/sdk-nested-classes/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/client-fetch/sdk-nested-classes/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/sdk/default/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/sdk/default/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/sdk/default/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/sdk/default/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/sdk/default/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/sdk/default/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/sdk/default/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/sdk/instance/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/sdk/instance/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/sdk/instance/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/sdk/instance/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/sdk/instance/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/sdk/instance/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/sdk/instance/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/sdk/throwOnError/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/sdk/throwOnError/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/sdk/throwOnError/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/sdk/throwOnError/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/sdk/throwOnError/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/sdk/throwOnError/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/sdk/throwOnError/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/transformers/type-format-valibot/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/transformers/type-format-valibot/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/transformers/type-format-valibot/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/transformers/type-format-valibot/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/transformers/type-format-valibot/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/transformers/type-format-valibot/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/transformers/type-format-valibot/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/transformers/type-format-zod/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/transformers/type-format-zod/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/transformers/type-format-zod/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/transformers/type-format-zod/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/transformers/type-format-zod/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/transformers/type-format-zod/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/transformers/type-format-zod/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/typescript/transforms-read-write-custom-name/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/typescript/transforms-read-write-custom-name/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/typescript/transforms-read-write-custom-name/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/typescript/transforms-read-write-custom-name/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/typescript/transforms-read-write-custom-name/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/typescript/transforms-read-write-custom-name/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/typescript/transforms-read-write-custom-name/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/typescript/transforms-read-write-ignore/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/typescript/transforms-read-write-ignore/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/typescript/transforms-read-write-ignore/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/typescript/transforms-read-write-ignore/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/typescript/transforms-read-write-ignore/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/typescript/transforms-read-write-ignore/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@hey-api/typescript/transforms-read-write-ignore/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@pinia/colada/asClass/@pinia/colada.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@pinia/colada/asClass/@pinia/colada.gen.ts
index a8d9f65a68..1d845eca9b 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@pinia/colada/asClass/@pinia/colada.gen.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@pinia/colada/asClass/@pinia/colada.gen.ts
@@ -1,16 +1,17 @@
 // This file is auto-generated by @hey-api/openapi-ts
 
-import type { _JSONValue, UseMutationOptions, UseQueryOptions } from '@pinia/colada';
+import { type _JSONValue, defineQueryOptions, type UseMutationOptions } from '@pinia/colada';
 
+import { serializeQueryKeyValue } from '../client';
 import { client } from '../client.gen';
 import { BarBazService, FooBazService, type Options } from '../sdk.gen';
-import type { FooBarPostData, FooBarPostResponse, FooBarPutData, FooBarPutResponse, FooPostData, FooPostResponse, FooPutData, FooPutResponse, GetFooBarData, GetFooBarResponse, GetFooData, GetFooResponse } from '../types.gen';
+import type { FooBarPostData, FooBarPostResponse, FooBarPutData, FooBarPutResponse, FooPostData, FooPostResponse, FooPutData, FooPutResponse, GetFooBarData, GetFooData } from '../types.gen';
 
 export type QueryKey<TOptions extends Options> = [
-    Pick<TOptions, 'body' | 'path'> & {
+    Pick<TOptions, 'path'> & {
         _id: string;
         baseUrl?: _JSONValue;
-        headers?: _JSONValue;
+        body?: _JSONValue;
         query?: _JSONValue;
         tags?: _JSONValue;
     }
@@ -21,19 +22,22 @@ const createQueryKey = <TOptions extends Options>(id: string, options?: TOptions
 ] => {
     const params: QueryKey<TOptions>[0] = { _id: id, baseUrl: options?.baseUrl || (options?.client ?? client).getConfig().baseUrl } as QueryKey<TOptions>[0];
     if (tags) {
-        params.tags = tags as unknown as undefined;
+        params.tags = tags as unknown as _JSONValue;
     }
-    if (options?.body) {
-        params.body = options.body;
-    }
-    if (options?.headers) {
-        params.headers = options.headers as unknown as undefined;
+    if (options?.body !== undefined) {
+        const normalizedBody = serializeQueryKeyValue(options.body);
+        if (normalizedBody !== undefined) {
+            params.body = normalizedBody;
+        }
     }
     if (options?.path) {
         params.path = options.path;
     }
-    if (options?.query) {
-        params.query = options.query as unknown as undefined;
+    if (options?.query !== undefined) {
+        const normalizedQuery = serializeQueryKeyValue(options.query);
+        if (normalizedQuery !== undefined) {
+            params.query = normalizedQuery;
+        }
     }
     return [
         params
@@ -42,19 +46,17 @@ const createQueryKey = <TOptions extends Options>(id: string, options?: TOptions
 
 export const getFooQueryKey = (options?: Options<GetFooData>) => createQueryKey('getFoo', options);
 
-export const getFooQuery = (options?: Options<GetFooData>): UseQueryOptions<GetFooResponse, Error> => {
-    return {
-        key: getFooQueryKey(options),
-        query: async (context) => {
-            const { data } = await FooBazService.getFoo({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const getFooQuery = defineQueryOptions((options?: Options<GetFooData>) => ({
+    key: getFooQueryKey(options),
+    query: async (context) => {
+        const { data } = await FooBazService.getFoo({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const fooPostMutation = (options?: Partial<Options<FooPostData>>): UseMutationOptions<FooPostResponse, Options<FooPostData>, Error> => {
     return {
@@ -84,19 +86,17 @@ export const fooPutMutation = (options?: Partial<Options<FooPutData>>): UseMutat
 
 export const getFooBarQueryKey = (options?: Options<GetFooBarData>) => createQueryKey('getFooBar', options);
 
-export const getFooBarQuery = (options?: Options<GetFooBarData>): UseQueryOptions<GetFooBarResponse, Error> => {
-    return {
-        key: getFooBarQueryKey(options),
-        query: async (context) => {
-            const { data } = await BarBazService.getFooBar({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const getFooBarQuery = defineQueryOptions((options?: Options<GetFooBarData>) => ({
+    key: getFooBarQueryKey(options),
+    query: async (context) => {
+        const { data } = await BarBazService.getFooBar({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const fooBarPostMutation = (options?: Partial<Options<FooBarPostData>>): UseMutationOptions<FooBarPostResponse, Options<FooBarPostData>, Error> => {
     return {
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@pinia/colada/asClass/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@pinia/colada/asClass/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@pinia/colada/asClass/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@pinia/colada/asClass/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@pinia/colada/asClass/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@pinia/colada/asClass/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@pinia/colada/asClass/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@pinia/colada/fetch/@pinia/colada.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@pinia/colada/fetch/@pinia/colada.gen.ts
index d30902d0be..b25e9919a4 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@pinia/colada/fetch/@pinia/colada.gen.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@pinia/colada/fetch/@pinia/colada.gen.ts
@@ -1,16 +1,17 @@
 // This file is auto-generated by @hey-api/openapi-ts
 
-import type { _JSONValue, UseMutationOptions, UseQueryOptions } from '@pinia/colada';
+import { type _JSONValue, defineQueryOptions, type UseMutationOptions } from '@pinia/colada';
 
+import { serializeQueryKeyValue } from '../client';
 import { client } from '../client.gen';
 import { callToTestOrderOfParams, callWithDefaultOptionalParameters, callWithDefaultParameters, callWithDescriptions, callWithDuplicateResponses, callWithNoContentResponse, callWithParameters, callWithResponse, callWithResponseAndNoContentResponse, callWithResponses, callWithResultFromHeader, callWithWeirdParameterNames, collectionFormat, complexTypes, deleteCallWithoutParametersAndResponse, dummyA, dummyB, duplicateName, duplicateName2, duplicateName3, duplicateName4, fooWow, getCallWithoutParametersAndResponse, nonAsciiæøåÆøÅöôêÊ字符串, type Options, patchApiVbyApiVersionNoTag, patchCallWithoutParametersAndResponse, postApiVbyApiVersionBody, postCallWithoutParametersAndResponse, putCallWithoutParametersAndResponse, serviceWithEmptyTag, testErrorCode, types } from '../sdk.gen';
-import type { CallToTestOrderOfParamsData, CallWithDefaultOptionalParametersData, CallWithDefaultParametersData, CallWithDescriptionsData, CallWithDuplicateResponsesData, CallWithDuplicateResponsesError, CallWithDuplicateResponsesResponse, CallWithNoContentResponseData, CallWithParametersData, CallWithResponseAndNoContentResponseData, CallWithResponseAndNoContentResponseResponse, CallWithResponseData, CallWithResponseResponse, CallWithResponsesData, CallWithResponsesError, CallWithResponsesResponse, CallWithResultFromHeaderData, CallWithWeirdParameterNamesData, CollectionFormatData, ComplexTypesData, ComplexTypesResponse, DeleteCallWithoutParametersAndResponseData, DummyAData, DummyBData, DuplicateName2Data, DuplicateName3Data, DuplicateName4Data, DuplicateNameData, FooWowData, GetCallWithoutParametersAndResponseData, NonAsciiæøåÆøÅöôêÊ字符串Data, NonAsciiæøåÆøÅöôêÊ字符串Response, PatchApiVbyApiVersionNoTagData, PatchCallWithoutParametersAndResponseData, PostApiVbyApiVersionBodyData, PostApiVbyApiVersionBodyError, PostApiVbyApiVersionBodyResponse, PostCallWithoutParametersAndResponseData, PutCallWithoutParametersAndResponseData, ServiceWithEmptyTagData, TestErrorCodeData, TypesData, TypesResponse } from '../types.gen';
+import type { CallToTestOrderOfParamsData, CallWithDefaultOptionalParametersData, CallWithDefaultParametersData, CallWithDescriptionsData, CallWithDuplicateResponsesData, CallWithDuplicateResponsesError, CallWithDuplicateResponsesResponse, CallWithNoContentResponseData, CallWithParametersData, CallWithResponseAndNoContentResponseData, CallWithResponseData, CallWithResponsesData, CallWithResponsesError, CallWithResponsesResponse, CallWithResultFromHeaderData, CallWithWeirdParameterNamesData, CollectionFormatData, ComplexTypesData, DeleteCallWithoutParametersAndResponseData, DummyAData, DummyBData, DuplicateName2Data, DuplicateName3Data, DuplicateName4Data, DuplicateNameData, FooWowData, GetCallWithoutParametersAndResponseData, NonAsciiæøåÆøÅöôêÊ字符串Data, NonAsciiæøåÆøÅöôêÊ字符串Response, PatchApiVbyApiVersionNoTagData, PatchCallWithoutParametersAndResponseData, PostApiVbyApiVersionBodyData, PostApiVbyApiVersionBodyError, PostApiVbyApiVersionBodyResponse, PostCallWithoutParametersAndResponseData, PutCallWithoutParametersAndResponseData, ServiceWithEmptyTagData, TestErrorCodeData, TypesData } from '../types.gen';
 
 export type QueryKey<TOptions extends Options> = [
-    Pick<TOptions, 'body' | 'path'> & {
+    Pick<TOptions, 'path'> & {
         _id: string;
         baseUrl?: _JSONValue;
-        headers?: _JSONValue;
+        body?: _JSONValue;
         query?: _JSONValue;
         tags?: _JSONValue;
     }
@@ -21,19 +22,22 @@ const createQueryKey = <TOptions extends Options>(id: string, options?: TOptions
 ] => {
     const params: QueryKey<TOptions>[0] = { _id: id, baseUrl: options?.baseUrl || (options?.client ?? client).getConfig().baseUrl } as QueryKey<TOptions>[0];
     if (tags) {
-        params.tags = tags as unknown as undefined;
+        params.tags = tags as unknown as _JSONValue;
     }
-    if (options?.body) {
-        params.body = options.body;
-    }
-    if (options?.headers) {
-        params.headers = options.headers as unknown as undefined;
+    if (options?.body !== undefined) {
+        const normalizedBody = serializeQueryKeyValue(options.body);
+        if (normalizedBody !== undefined) {
+            params.body = normalizedBody;
+        }
     }
     if (options?.path) {
         params.path = options.path;
     }
-    if (options?.query) {
-        params.query = options.query as unknown as undefined;
+    if (options?.query !== undefined) {
+        const normalizedQuery = serializeQueryKeyValue(options.query);
+        if (normalizedQuery !== undefined) {
+            params.query = normalizedQuery;
+        }
     }
     return [
         params
@@ -42,19 +46,17 @@ const createQueryKey = <TOptions extends Options>(id: string, options?: TOptions
 
 export const serviceWithEmptyTagQueryKey = (options?: Options<ServiceWithEmptyTagData>) => createQueryKey('serviceWithEmptyTag', options);
 
-export const serviceWithEmptyTagQuery = (options?: Options<ServiceWithEmptyTagData>): UseQueryOptions<unknown, Error> => {
-    return {
-        key: serviceWithEmptyTagQueryKey(options),
-        query: async (context) => {
-            const { data } = await serviceWithEmptyTag({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const serviceWithEmptyTagQuery = defineQueryOptions((options?: Options<ServiceWithEmptyTagData>) => ({
+    key: serviceWithEmptyTagQueryKey(options),
+    query: async (context) => {
+        const { data } = await serviceWithEmptyTag({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const patchApiVbyApiVersionNoTagMutation = (options?: Partial<Options<PatchApiVbyApiVersionNoTagData>>): UseMutationOptions<unknown, Options<PatchApiVbyApiVersionNoTagData>, Error> => {
     return {
@@ -97,19 +99,17 @@ export const deleteCallWithoutParametersAndResponseMutation = (options?: Partial
 
 export const getCallWithoutParametersAndResponseQueryKey = (options?: Options<GetCallWithoutParametersAndResponseData>) => createQueryKey('getCallWithoutParametersAndResponse', options);
 
-export const getCallWithoutParametersAndResponseQuery = (options?: Options<GetCallWithoutParametersAndResponseData>): UseQueryOptions<unknown, Error> => {
-    return {
-        key: getCallWithoutParametersAndResponseQueryKey(options),
-        query: async (context) => {
-            const { data } = await getCallWithoutParametersAndResponse({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const getCallWithoutParametersAndResponseQuery = defineQueryOptions((options?: Options<GetCallWithoutParametersAndResponseData>) => ({
+    key: getCallWithoutParametersAndResponseQueryKey(options),
+    query: async (context) => {
+        const { data } = await getCallWithoutParametersAndResponse({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const patchCallWithoutParametersAndResponseMutation = (options?: Partial<Options<PatchCallWithoutParametersAndResponseData>>): UseMutationOptions<unknown, Options<PatchCallWithoutParametersAndResponseData>, Error> => {
     return {
@@ -191,19 +191,17 @@ export const callWithWeirdParameterNamesMutation = (options?: Partial<Options<Ca
 
 export const callWithDefaultParametersQueryKey = (options: Options<CallWithDefaultParametersData>) => createQueryKey('callWithDefaultParameters', options);
 
-export const callWithDefaultParametersQuery = (options: Options<CallWithDefaultParametersData>): UseQueryOptions<unknown, Error> => {
-    return {
-        key: callWithDefaultParametersQueryKey(options),
-        query: async (context) => {
-            const { data } = await callWithDefaultParameters({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const callWithDefaultParametersQuery = defineQueryOptions((options: Options<CallWithDefaultParametersData>) => ({
+    key: callWithDefaultParametersQueryKey(options),
+    query: async (context) => {
+        const { data } = await callWithDefaultParameters({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const callWithDefaultOptionalParametersMutation = (options?: Partial<Options<CallWithDefaultOptionalParametersData>>): UseMutationOptions<unknown, Options<CallWithDefaultOptionalParametersData>, Error> => {
     return {
@@ -246,19 +244,17 @@ export const duplicateNameMutation = (options?: Partial<Options<DuplicateNameDat
 
 export const duplicateName2QueryKey = (options?: Options<DuplicateName2Data>) => createQueryKey('duplicateName2', options);
 
-export const duplicateName2Query = (options?: Options<DuplicateName2Data>): UseQueryOptions<unknown, Error> => {
-    return {
-        key: duplicateName2QueryKey(options),
-        query: async (context) => {
-            const { data } = await duplicateName2({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const duplicateName2Query = defineQueryOptions((options?: Options<DuplicateName2Data>) => ({
+    key: duplicateName2QueryKey(options),
+    query: async (context) => {
+        const { data } = await duplicateName2({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const duplicateName3Mutation = (options?: Partial<Options<DuplicateName3Data>>): UseMutationOptions<unknown, Options<DuplicateName3Data>, Error> => {
     return {
@@ -288,83 +284,73 @@ export const duplicateName4Mutation = (options?: Partial<Options<DuplicateName4D
 
 export const callWithNoContentResponseQueryKey = (options?: Options<CallWithNoContentResponseData>) => createQueryKey('callWithNoContentResponse', options);
 
-export const callWithNoContentResponseQuery = (options?: Options<CallWithNoContentResponseData>): UseQueryOptions<unknown, Error> => {
-    return {
-        key: callWithNoContentResponseQueryKey(options),
-        query: async (context) => {
-            const { data } = await callWithNoContentResponse({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const callWithNoContentResponseQuery = defineQueryOptions((options?: Options<CallWithNoContentResponseData>) => ({
+    key: callWithNoContentResponseQueryKey(options),
+    query: async (context) => {
+        const { data } = await callWithNoContentResponse({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const callWithResponseAndNoContentResponseQueryKey = (options?: Options<CallWithResponseAndNoContentResponseData>) => createQueryKey('callWithResponseAndNoContentResponse', options);
 
-export const callWithResponseAndNoContentResponseQuery = (options?: Options<CallWithResponseAndNoContentResponseData>): UseQueryOptions<CallWithResponseAndNoContentResponseResponse, Error> => {
-    return {
-        key: callWithResponseAndNoContentResponseQueryKey(options),
-        query: async (context) => {
-            const { data } = await callWithResponseAndNoContentResponse({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const callWithResponseAndNoContentResponseQuery = defineQueryOptions((options?: Options<CallWithResponseAndNoContentResponseData>) => ({
+    key: callWithResponseAndNoContentResponseQueryKey(options),
+    query: async (context) => {
+        const { data } = await callWithResponseAndNoContentResponse({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const dummyAQueryKey = (options?: Options<DummyAData>) => createQueryKey('dummyA', options);
 
-export const dummyAQuery = (options?: Options<DummyAData>): UseQueryOptions<unknown, Error> => {
-    return {
-        key: dummyAQueryKey(options),
-        query: async (context) => {
-            const { data } = await dummyA({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const dummyAQuery = defineQueryOptions((options?: Options<DummyAData>) => ({
+    key: dummyAQueryKey(options),
+    query: async (context) => {
+        const { data } = await dummyA({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const dummyBQueryKey = (options?: Options<DummyBData>) => createQueryKey('dummyB', options);
 
-export const dummyBQuery = (options?: Options<DummyBData>): UseQueryOptions<unknown, Error> => {
-    return {
-        key: dummyBQueryKey(options),
-        query: async (context) => {
-            const { data } = await dummyB({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const dummyBQuery = defineQueryOptions((options?: Options<DummyBData>) => ({
+    key: dummyBQueryKey(options),
+    query: async (context) => {
+        const { data } = await dummyB({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const callWithResponseQueryKey = (options?: Options<CallWithResponseData>) => createQueryKey('callWithResponse', options);
 
-export const callWithResponseQuery = (options?: Options<CallWithResponseData>): UseQueryOptions<CallWithResponseResponse, Error> => {
-    return {
-        key: callWithResponseQueryKey(options),
-        query: async (context) => {
-            const { data } = await callWithResponse({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const callWithResponseQuery = defineQueryOptions((options?: Options<CallWithResponseData>) => ({
+    key: callWithResponseQueryKey(options),
+    query: async (context) => {
+        const { data } = await callWithResponse({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const callWithDuplicateResponsesMutation = (options?: Partial<Options<CallWithDuplicateResponsesData>>): UseMutationOptions<CallWithDuplicateResponsesResponse, Options<CallWithDuplicateResponsesData>, CallWithDuplicateResponsesError> => {
     return {
@@ -394,51 +380,45 @@ export const callWithResponsesMutation = (options?: Partial<Options<CallWithResp
 
 export const collectionFormatQueryKey = (options: Options<CollectionFormatData>) => createQueryKey('collectionFormat', options);
 
-export const collectionFormatQuery = (options: Options<CollectionFormatData>): UseQueryOptions<unknown, Error> => {
-    return {
-        key: collectionFormatQueryKey(options),
-        query: async (context) => {
-            const { data } = await collectionFormat({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const collectionFormatQuery = defineQueryOptions((options: Options<CollectionFormatData>) => ({
+    key: collectionFormatQueryKey(options),
+    query: async (context) => {
+        const { data } = await collectionFormat({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const typesQueryKey = (options: Options<TypesData>) => createQueryKey('types', options);
 
-export const typesQuery = (options: Options<TypesData>): UseQueryOptions<TypesResponse, Error> => {
-    return {
-        key: typesQueryKey(options),
-        query: async (context) => {
-            const { data } = await types({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const typesQuery = defineQueryOptions((options: Options<TypesData>) => ({
+    key: typesQueryKey(options),
+    query: async (context) => {
+        const { data } = await types({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const complexTypesQueryKey = (options: Options<ComplexTypesData>) => createQueryKey('complexTypes', options);
 
-export const complexTypesQuery = (options: Options<ComplexTypesData>): UseQueryOptions<ComplexTypesResponse, Error> => {
-    return {
-        key: complexTypesQueryKey(options),
-        query: async (context) => {
-            const { data } = await complexTypes({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const complexTypesQuery = defineQueryOptions((options: Options<ComplexTypesData>) => ({
+    key: complexTypesQueryKey(options),
+    query: async (context) => {
+        const { data } = await complexTypes({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const callWithResultFromHeaderMutation = (options?: Partial<Options<CallWithResultFromHeaderData>>): UseMutationOptions<unknown, Options<CallWithResultFromHeaderData>, Error> => {
     return {
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@pinia/colada/fetch/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@pinia/colada/fetch/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@pinia/colada/fetch/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@pinia/colada/fetch/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@pinia/colada/fetch/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@pinia/colada/fetch/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@pinia/colada/fetch/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/angular-query-experimental/asClass/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/angular-query-experimental/asClass/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/angular-query-experimental/asClass/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/angular-query-experimental/asClass/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/angular-query-experimental/asClass/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/angular-query-experimental/asClass/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/angular-query-experimental/asClass/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/angular-query-experimental/axios/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/angular-query-experimental/axios/client/index.ts
index 8ddc04f425..cff1d39c90 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/angular-query-experimental/axios/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/angular-query-experimental/axios/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/angular-query-experimental/axios/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/angular-query-experimental/axios/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/angular-query-experimental/axios/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/angular-query-experimental/fetch/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/angular-query-experimental/fetch/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/angular-query-experimental/fetch/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/angular-query-experimental/fetch/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/angular-query-experimental/fetch/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/angular-query-experimental/fetch/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/angular-query-experimental/fetch/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/angular-query-experimental/name-builder/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/angular-query-experimental/name-builder/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/angular-query-experimental/name-builder/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/angular-query-experimental/name-builder/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/angular-query-experimental/name-builder/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/angular-query-experimental/name-builder/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/angular-query-experimental/name-builder/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/react-query/asClass/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/react-query/asClass/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/react-query/asClass/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/react-query/asClass/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/react-query/asClass/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/react-query/asClass/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/react-query/asClass/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/react-query/axios/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/react-query/axios/client/index.ts
index 8ddc04f425..cff1d39c90 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/react-query/axios/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/react-query/axios/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/react-query/axios/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/react-query/axios/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/react-query/axios/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/react-query/fetch/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/react-query/fetch/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/react-query/fetch/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/react-query/fetch/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/react-query/fetch/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/react-query/fetch/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/react-query/fetch/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/react-query/name-builder/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/react-query/name-builder/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/react-query/name-builder/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/react-query/name-builder/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/react-query/name-builder/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/react-query/name-builder/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/react-query/name-builder/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/solid-query/asClass/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/solid-query/asClass/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/solid-query/asClass/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/solid-query/asClass/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/solid-query/asClass/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/solid-query/asClass/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/solid-query/asClass/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/solid-query/axios/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/solid-query/axios/client/index.ts
index 8ddc04f425..cff1d39c90 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/solid-query/axios/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/solid-query/axios/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/solid-query/axios/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/solid-query/axios/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/solid-query/axios/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/solid-query/fetch/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/solid-query/fetch/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/solid-query/fetch/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/solid-query/fetch/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/solid-query/fetch/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/solid-query/fetch/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/solid-query/fetch/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/solid-query/name-builder/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/solid-query/name-builder/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/solid-query/name-builder/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/solid-query/name-builder/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/solid-query/name-builder/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/solid-query/name-builder/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/solid-query/name-builder/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/svelte-query/asClass/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/svelte-query/asClass/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/svelte-query/asClass/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/svelte-query/asClass/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/svelte-query/asClass/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/svelte-query/asClass/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/svelte-query/asClass/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/svelte-query/axios/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/svelte-query/axios/client/index.ts
index 8ddc04f425..cff1d39c90 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/svelte-query/axios/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/svelte-query/axios/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/svelte-query/axios/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/svelte-query/axios/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/svelte-query/axios/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/svelte-query/fetch/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/svelte-query/fetch/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/svelte-query/fetch/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/svelte-query/fetch/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/svelte-query/fetch/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/svelte-query/fetch/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/svelte-query/fetch/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/svelte-query/name-builder/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/svelte-query/name-builder/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/svelte-query/name-builder/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/svelte-query/name-builder/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/svelte-query/name-builder/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/svelte-query/name-builder/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/svelte-query/name-builder/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/vue-query/asClass/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/vue-query/asClass/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/vue-query/asClass/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/vue-query/asClass/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/vue-query/asClass/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/vue-query/asClass/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/vue-query/asClass/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/vue-query/axios/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/vue-query/axios/client/index.ts
index 8ddc04f425..cff1d39c90 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/vue-query/axios/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/vue-query/axios/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/vue-query/axios/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/vue-query/axios/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/vue-query/axios/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/vue-query/fetch/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/vue-query/fetch/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/vue-query/fetch/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/vue-query/fetch/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/vue-query/fetch/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/vue-query/fetch/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/vue-query/fetch/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/vue-query/name-builder/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/vue-query/name-builder/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/vue-query/name-builder/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/vue-query/name-builder/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/vue-query/name-builder/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/vue-query/name-builder/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/plugins/@tanstack/vue-query/name-builder/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/schema-unknown/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/schema-unknown/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/schema-unknown/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/schema-unknown/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/schema-unknown/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/schema-unknown/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/schema-unknown/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/security-api-key/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/security-api-key/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/security-api-key/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/security-api-key/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/security-api-key/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/security-api-key/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/security-api-key/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/security-basic/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/security-basic/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/security-basic/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/security-basic/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/security-basic/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/security-basic/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/security-basic/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/security-false/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/security-false/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/security-false/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/security-false/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/security-false/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/security-false/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/security-false/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/security-oauth2/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/security-oauth2/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/security-oauth2/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/security-oauth2/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/security-oauth2/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/security-oauth2/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/security-oauth2/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/servers-base-path/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/servers-base-path/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/servers-base-path/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/servers-base-path/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/servers-base-path/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/servers-base-path/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/servers-base-path/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/servers-host/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/servers-host/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/servers-host/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/servers-host/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/servers-host/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/servers-host/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/servers-host/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/servers/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/servers/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/servers/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/servers/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/servers/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/servers/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/servers/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/transforms-read-write/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/transforms-read-write/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/transforms-read-write/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/transforms-read-write/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/transforms-read-write/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/transforms-read-write/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/transforms-read-write/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/body-response-text-plain/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/body-response-text-plain/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/body-response-text-plain/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/body-response-text-plain/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/body-response-text-plain/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/body-response-text-plain/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/body-response-text-plain/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/content-types/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/content-types/client/index.ts
index 8ddc04f425..cff1d39c90 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/content-types/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/content-types/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/content-types/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/content-types/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/content-types/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/internal-name-conflict/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/internal-name-conflict/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/internal-name-conflict/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/internal-name-conflict/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/internal-name-conflict/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/internal-name-conflict/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/internal-name-conflict/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/parameter-explode-false-axios/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/parameter-explode-false-axios/client/index.ts
index 8ddc04f425..cff1d39c90 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/parameter-explode-false-axios/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/parameter-explode-false-axios/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/parameter-explode-false-axios/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/parameter-explode-false-axios/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/parameter-explode-false-axios/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/parameter-explode-false/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/parameter-explode-false/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/parameter-explode-false/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/parameter-explode-false/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/parameter-explode-false/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/parameter-explode-false/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/parameter-explode-false/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@angular/common/default-class/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@angular/common/default-class/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@angular/common/default-class/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@angular/common/default-class/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@angular/common/default-class/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@angular/common/default-class/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@angular/common/default-class/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@angular/common/default/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@angular/common/default/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@angular/common/default/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@angular/common/default/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@angular/common/default/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@angular/common/default/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@angular/common/default/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/client-fetch/sdk-nested-classes-instance/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/client-fetch/sdk-nested-classes-instance/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/client-fetch/sdk-nested-classes-instance/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/client-fetch/sdk-nested-classes-instance/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/client-fetch/sdk-nested-classes-instance/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/client-fetch/sdk-nested-classes-instance/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/client-fetch/sdk-nested-classes-instance/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/client-fetch/sdk-nested-classes/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/client-fetch/sdk-nested-classes/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/client-fetch/sdk-nested-classes/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/client-fetch/sdk-nested-classes/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/client-fetch/sdk-nested-classes/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/client-fetch/sdk-nested-classes/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/client-fetch/sdk-nested-classes/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/sdk/default/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/sdk/default/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/sdk/default/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/sdk/default/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/sdk/default/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/sdk/default/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/sdk/default/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/sdk/instance/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/sdk/instance/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/sdk/instance/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/sdk/instance/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/sdk/instance/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/sdk/instance/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/sdk/instance/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/sdk/throwOnError/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/sdk/throwOnError/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/sdk/throwOnError/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/sdk/throwOnError/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/sdk/throwOnError/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/sdk/throwOnError/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/sdk/throwOnError/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/transformers/type-format-valibot/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/transformers/type-format-valibot/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/transformers/type-format-valibot/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/transformers/type-format-valibot/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/transformers/type-format-valibot/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/transformers/type-format-valibot/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/transformers/type-format-valibot/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/transformers/type-format-zod/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/transformers/type-format-zod/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/transformers/type-format-zod/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/transformers/type-format-zod/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/transformers/type-format-zod/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/transformers/type-format-zod/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/transformers/type-format-zod/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/typescript/transforms-read-write-custom-name/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/typescript/transforms-read-write-custom-name/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/typescript/transforms-read-write-custom-name/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/typescript/transforms-read-write-custom-name/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/typescript/transforms-read-write-custom-name/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/typescript/transforms-read-write-custom-name/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/typescript/transforms-read-write-custom-name/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/typescript/transforms-read-write-ignore/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/typescript/transforms-read-write-ignore/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/typescript/transforms-read-write-ignore/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/typescript/transforms-read-write-ignore/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/typescript/transforms-read-write-ignore/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/typescript/transforms-read-write-ignore/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/typescript/transforms-read-write-ignore/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@pinia/colada/asClass/@pinia/colada.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@pinia/colada/asClass/@pinia/colada.gen.ts
index a8d9f65a68..1d845eca9b 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@pinia/colada/asClass/@pinia/colada.gen.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@pinia/colada/asClass/@pinia/colada.gen.ts
@@ -1,16 +1,17 @@
 // This file is auto-generated by @hey-api/openapi-ts
 
-import type { _JSONValue, UseMutationOptions, UseQueryOptions } from '@pinia/colada';
+import { type _JSONValue, defineQueryOptions, type UseMutationOptions } from '@pinia/colada';
 
+import { serializeQueryKeyValue } from '../client';
 import { client } from '../client.gen';
 import { BarBazService, FooBazService, type Options } from '../sdk.gen';
-import type { FooBarPostData, FooBarPostResponse, FooBarPutData, FooBarPutResponse, FooPostData, FooPostResponse, FooPutData, FooPutResponse, GetFooBarData, GetFooBarResponse, GetFooData, GetFooResponse } from '../types.gen';
+import type { FooBarPostData, FooBarPostResponse, FooBarPutData, FooBarPutResponse, FooPostData, FooPostResponse, FooPutData, FooPutResponse, GetFooBarData, GetFooData } from '../types.gen';
 
 export type QueryKey<TOptions extends Options> = [
-    Pick<TOptions, 'body' | 'path'> & {
+    Pick<TOptions, 'path'> & {
         _id: string;
         baseUrl?: _JSONValue;
-        headers?: _JSONValue;
+        body?: _JSONValue;
         query?: _JSONValue;
         tags?: _JSONValue;
     }
@@ -21,19 +22,22 @@ const createQueryKey = <TOptions extends Options>(id: string, options?: TOptions
 ] => {
     const params: QueryKey<TOptions>[0] = { _id: id, baseUrl: options?.baseUrl || (options?.client ?? client).getConfig().baseUrl } as QueryKey<TOptions>[0];
     if (tags) {
-        params.tags = tags as unknown as undefined;
+        params.tags = tags as unknown as _JSONValue;
     }
-    if (options?.body) {
-        params.body = options.body;
-    }
-    if (options?.headers) {
-        params.headers = options.headers as unknown as undefined;
+    if (options?.body !== undefined) {
+        const normalizedBody = serializeQueryKeyValue(options.body);
+        if (normalizedBody !== undefined) {
+            params.body = normalizedBody;
+        }
     }
     if (options?.path) {
         params.path = options.path;
     }
-    if (options?.query) {
-        params.query = options.query as unknown as undefined;
+    if (options?.query !== undefined) {
+        const normalizedQuery = serializeQueryKeyValue(options.query);
+        if (normalizedQuery !== undefined) {
+            params.query = normalizedQuery;
+        }
     }
     return [
         params
@@ -42,19 +46,17 @@ const createQueryKey = <TOptions extends Options>(id: string, options?: TOptions
 
 export const getFooQueryKey = (options?: Options<GetFooData>) => createQueryKey('getFoo', options);
 
-export const getFooQuery = (options?: Options<GetFooData>): UseQueryOptions<GetFooResponse, Error> => {
-    return {
-        key: getFooQueryKey(options),
-        query: async (context) => {
-            const { data } = await FooBazService.getFoo({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const getFooQuery = defineQueryOptions((options?: Options<GetFooData>) => ({
+    key: getFooQueryKey(options),
+    query: async (context) => {
+        const { data } = await FooBazService.getFoo({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const fooPostMutation = (options?: Partial<Options<FooPostData>>): UseMutationOptions<FooPostResponse, Options<FooPostData>, Error> => {
     return {
@@ -84,19 +86,17 @@ export const fooPutMutation = (options?: Partial<Options<FooPutData>>): UseMutat
 
 export const getFooBarQueryKey = (options?: Options<GetFooBarData>) => createQueryKey('getFooBar', options);
 
-export const getFooBarQuery = (options?: Options<GetFooBarData>): UseQueryOptions<GetFooBarResponse, Error> => {
-    return {
-        key: getFooBarQueryKey(options),
-        query: async (context) => {
-            const { data } = await BarBazService.getFooBar({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const getFooBarQuery = defineQueryOptions((options?: Options<GetFooBarData>) => ({
+    key: getFooBarQueryKey(options),
+    query: async (context) => {
+        const { data } = await BarBazService.getFooBar({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const fooBarPostMutation = (options?: Partial<Options<FooBarPostData>>): UseMutationOptions<FooBarPostResponse, Options<FooBarPostData>, Error> => {
     return {
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@pinia/colada/asClass/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@pinia/colada/asClass/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@pinia/colada/asClass/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@pinia/colada/asClass/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@pinia/colada/asClass/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@pinia/colada/asClass/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@pinia/colada/asClass/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@pinia/colada/fetch/@pinia/colada.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@pinia/colada/fetch/@pinia/colada.gen.ts
index 593b8e81ab..5f822ac96f 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@pinia/colada/fetch/@pinia/colada.gen.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@pinia/colada/fetch/@pinia/colada.gen.ts
@@ -1,16 +1,17 @@
 // This file is auto-generated by @hey-api/openapi-ts
 
-import type { _JSONValue, UseMutationOptions, UseQueryOptions } from '@pinia/colada';
+import { type _JSONValue, defineQueryOptions, type UseMutationOptions } from '@pinia/colada';
 
+import { serializeQueryKeyValue } from '../client';
 import { client } from '../client.gen';
 import { apiVVersionODataControllerCount, callToTestOrderOfParams, callWithDefaultOptionalParameters, callWithDefaultParameters, callWithDescriptions, callWithDuplicateResponses, callWithNoContentResponse, callWithParameters, callWithResponse, callWithResponseAndNoContentResponse, callWithResponses, callWithResultFromHeader, callWithWeirdParameterNames, collectionFormat, complexParams, complexTypes, deleteCallWithoutParametersAndResponse, deleteFoo, deprecatedCall, dummyA, dummyB, duplicateName, duplicateName2, duplicateName3, duplicateName4, export_, fileResponse, fooWow, getApiVbyApiVersionSimpleOperation, getCallWithOptionalParam, getCallWithoutParametersAndResponse, import_, multipartRequest, multipartResponse, nonAsciiæøåÆøÅöôêÊ字符串, type Options, patchApiVbyApiVersionNoTag, patchCallWithoutParametersAndResponse, postApiVbyApiVersionFormData, postApiVbyApiVersionRequestBody, postCallWithOptionalParam, postCallWithoutParametersAndResponse, putCallWithoutParametersAndResponse, putWithFormUrlEncoded, testErrorCode, types, uploadFile } from '../sdk.gen';
-import type { ApiVVersionODataControllerCountData, ApiVVersionODataControllerCountResponse, CallToTestOrderOfParamsData, CallWithDefaultOptionalParametersData, CallWithDefaultParametersData, CallWithDescriptionsData, CallWithDuplicateResponsesData, CallWithDuplicateResponsesError, CallWithDuplicateResponsesResponse, CallWithNoContentResponseData, CallWithNoContentResponseResponse, CallWithParametersData, CallWithResponseAndNoContentResponseData, CallWithResponseAndNoContentResponseResponse, CallWithResponseData, CallWithResponseResponse, CallWithResponsesData, CallWithResponsesError, CallWithResponsesResponse, CallWithResultFromHeaderData, CallWithWeirdParameterNamesData, CollectionFormatData, ComplexParamsData, ComplexParamsResponse, ComplexTypesData, ComplexTypesResponse, DeleteCallWithoutParametersAndResponseData, DeleteFooData3, DeprecatedCallData, DummyAData, DummyAResponse, DummyBData, DummyBResponse, DuplicateName2Data, DuplicateName3Data, DuplicateName4Data, DuplicateNameData, ExportData, FileResponseData, FileResponseResponse, FooWowData, GetApiVbyApiVersionSimpleOperationData, GetApiVbyApiVersionSimpleOperationError, GetApiVbyApiVersionSimpleOperationResponse, GetCallWithOptionalParamData, GetCallWithoutParametersAndResponseData, ImportData, ImportResponse, MultipartRequestData, MultipartResponseData, MultipartResponseResponse, NonAsciiæøåÆøÅöôêÊ字符串Data, NonAsciiæøåÆøÅöôêÊ字符串Response, PatchApiVbyApiVersionNoTagData, PatchCallWithoutParametersAndResponseData, PostApiVbyApiVersionFormDataData, PostApiVbyApiVersionRequestBodyData, PostCallWithOptionalParamData, PostCallWithOptionalParamResponse, PostCallWithoutParametersAndResponseData, PutCallWithoutParametersAndResponseData, PutWithFormUrlEncodedData, TestErrorCodeData, TypesData, TypesResponse, UploadFileData, UploadFileResponse } from '../types.gen';
+import type { ApiVVersionODataControllerCountData, CallToTestOrderOfParamsData, CallWithDefaultOptionalParametersData, CallWithDefaultParametersData, CallWithDescriptionsData, CallWithDuplicateResponsesData, CallWithDuplicateResponsesError, CallWithDuplicateResponsesResponse, CallWithNoContentResponseData, CallWithParametersData, CallWithResponseAndNoContentResponseData, CallWithResponseData, CallWithResponsesData, CallWithResponsesError, CallWithResponsesResponse, CallWithResultFromHeaderData, CallWithWeirdParameterNamesData, CollectionFormatData, ComplexParamsData, ComplexParamsResponse, ComplexTypesData, DeleteCallWithoutParametersAndResponseData, DeleteFooData3, DeprecatedCallData, DummyAData, DummyBData, DuplicateName2Data, DuplicateName3Data, DuplicateName4Data, DuplicateNameData, ExportData, FileResponseData, FooWowData, GetApiVbyApiVersionSimpleOperationData, GetCallWithOptionalParamData, GetCallWithoutParametersAndResponseData, ImportData, ImportResponse, MultipartRequestData, MultipartResponseData, NonAsciiæøåÆøÅöôêÊ字符串Data, NonAsciiæøåÆøÅöôêÊ字符串Response, PatchApiVbyApiVersionNoTagData, PatchCallWithoutParametersAndResponseData, PostApiVbyApiVersionFormDataData, PostApiVbyApiVersionRequestBodyData, PostCallWithOptionalParamData, PostCallWithOptionalParamResponse, PostCallWithoutParametersAndResponseData, PutCallWithoutParametersAndResponseData, PutWithFormUrlEncodedData, TestErrorCodeData, TypesData, UploadFileData, UploadFileResponse } from '../types.gen';
 
 export type QueryKey<TOptions extends Options> = [
-    Pick<TOptions, 'body' | 'path'> & {
+    Pick<TOptions, 'path'> & {
         _id: string;
         baseUrl?: _JSONValue;
-        headers?: _JSONValue;
+        body?: _JSONValue;
         query?: _JSONValue;
         tags?: _JSONValue;
     }
@@ -21,19 +22,22 @@ const createQueryKey = <TOptions extends Options>(id: string, options?: TOptions
 ] => {
     const params: QueryKey<TOptions>[0] = { _id: id, baseUrl: options?.baseUrl || (options?.client ?? client).getConfig().baseUrl } as QueryKey<TOptions>[0];
     if (tags) {
-        params.tags = tags as unknown as undefined;
+        params.tags = tags as unknown as _JSONValue;
     }
-    if (options?.body) {
-        params.body = options.body;
-    }
-    if (options?.headers) {
-        params.headers = options.headers as unknown as undefined;
+    if (options?.body !== undefined) {
+        const normalizedBody = serializeQueryKeyValue(options.body);
+        if (normalizedBody !== undefined) {
+            params.body = normalizedBody;
+        }
     }
     if (options?.path) {
         params.path = options.path;
     }
-    if (options?.query) {
-        params.query = options.query as unknown as undefined;
+    if (options?.query !== undefined) {
+        const normalizedQuery = serializeQueryKeyValue(options.query);
+        if (normalizedQuery !== undefined) {
+            params.query = normalizedQuery;
+        }
     }
     return [
         params
@@ -42,19 +46,17 @@ const createQueryKey = <TOptions extends Options>(id: string, options?: TOptions
 
 export const exportQueryKey = (options?: Options<ExportData>) => createQueryKey('export', options);
 
-export const exportQuery = (options?: Options<ExportData>): UseQueryOptions<unknown, Error> => {
-    return {
-        key: exportQueryKey(options),
-        query: async (context) => {
-            const { data } = await export_({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const exportQuery = defineQueryOptions((options?: Options<ExportData>) => ({
+    key: exportQueryKey(options),
+    query: async (context) => {
+        const { data } = await export_({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const patchApiVbyApiVersionNoTagMutation = (options?: Partial<Options<PatchApiVbyApiVersionNoTagData>>): UseMutationOptions<unknown, Options<PatchApiVbyApiVersionNoTagData>, Error> => {
     return {
@@ -97,35 +99,31 @@ export const fooWowMutation = (options?: Partial<Options<FooWowData>>): UseMutat
 
 export const apiVVersionODataControllerCountQueryKey = (options?: Options<ApiVVersionODataControllerCountData>) => createQueryKey('apiVVersionODataControllerCount', options);
 
-export const apiVVersionODataControllerCountQuery = (options?: Options<ApiVVersionODataControllerCountData>): UseQueryOptions<ApiVVersionODataControllerCountResponse, Error> => {
-    return {
-        key: apiVVersionODataControllerCountQueryKey(options),
-        query: async (context) => {
-            const { data } = await apiVVersionODataControllerCount({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const apiVVersionODataControllerCountQuery = defineQueryOptions((options?: Options<ApiVVersionODataControllerCountData>) => ({
+    key: apiVVersionODataControllerCountQueryKey(options),
+    query: async (context) => {
+        const { data } = await apiVVersionODataControllerCount({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const getApiVbyApiVersionSimpleOperationQueryKey = (options: Options<GetApiVbyApiVersionSimpleOperationData>) => createQueryKey('getApiVbyApiVersionSimpleOperation', options);
 
-export const getApiVbyApiVersionSimpleOperationQuery = (options: Options<GetApiVbyApiVersionSimpleOperationData>): UseQueryOptions<GetApiVbyApiVersionSimpleOperationResponse, GetApiVbyApiVersionSimpleOperationError> => {
-    return {
-        key: getApiVbyApiVersionSimpleOperationQueryKey(options),
-        query: async (context) => {
-            const { data } = await getApiVbyApiVersionSimpleOperation({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const getApiVbyApiVersionSimpleOperationQuery = defineQueryOptions((options: Options<GetApiVbyApiVersionSimpleOperationData>) => ({
+    key: getApiVbyApiVersionSimpleOperationQueryKey(options),
+    query: async (context) => {
+        const { data } = await getApiVbyApiVersionSimpleOperation({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const deleteCallWithoutParametersAndResponseMutation = (options?: Partial<Options<DeleteCallWithoutParametersAndResponseData>>): UseMutationOptions<unknown, Options<DeleteCallWithoutParametersAndResponseData>, Error> => {
     return {
@@ -142,19 +140,17 @@ export const deleteCallWithoutParametersAndResponseMutation = (options?: Partial
 
 export const getCallWithoutParametersAndResponseQueryKey = (options?: Options<GetCallWithoutParametersAndResponseData>) => createQueryKey('getCallWithoutParametersAndResponse', options);
 
-export const getCallWithoutParametersAndResponseQuery = (options?: Options<GetCallWithoutParametersAndResponseData>): UseQueryOptions<unknown, Error> => {
-    return {
-        key: getCallWithoutParametersAndResponseQueryKey(options),
-        query: async (context) => {
-            const { data } = await getCallWithoutParametersAndResponse({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const getCallWithoutParametersAndResponseQuery = defineQueryOptions((options?: Options<GetCallWithoutParametersAndResponseData>) => ({
+    key: getCallWithoutParametersAndResponseQueryKey(options),
+    query: async (context) => {
+        const { data } = await getCallWithoutParametersAndResponse({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const patchCallWithoutParametersAndResponseMutation = (options?: Partial<Options<PatchCallWithoutParametersAndResponseData>>): UseMutationOptions<unknown, Options<PatchCallWithoutParametersAndResponseData>, Error> => {
     return {
@@ -265,19 +261,17 @@ export const callWithWeirdParameterNamesMutation = (options?: Partial<Options<Ca
 
 export const getCallWithOptionalParamQueryKey = (options: Options<GetCallWithOptionalParamData>) => createQueryKey('getCallWithOptionalParam', options);
 
-export const getCallWithOptionalParamQuery = (options: Options<GetCallWithOptionalParamData>): UseQueryOptions<unknown, Error> => {
-    return {
-        key: getCallWithOptionalParamQueryKey(options),
-        query: async (context) => {
-            const { data } = await getCallWithOptionalParam({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const getCallWithOptionalParamQuery = defineQueryOptions((options: Options<GetCallWithOptionalParamData>) => ({
+    key: getCallWithOptionalParamQueryKey(options),
+    query: async (context) => {
+        const { data } = await getCallWithOptionalParam({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const postCallWithOptionalParamMutation = (options?: Partial<Options<PostCallWithOptionalParamData>>): UseMutationOptions<PostCallWithOptionalParamResponse, Options<PostCallWithOptionalParamData>, Error> => {
     return {
@@ -320,19 +314,17 @@ export const postApiVbyApiVersionFormDataMutation = (options?: Partial<Options<P
 
 export const callWithDefaultParametersQueryKey = (options?: Options<CallWithDefaultParametersData>) => createQueryKey('callWithDefaultParameters', options);
 
-export const callWithDefaultParametersQuery = (options?: Options<CallWithDefaultParametersData>): UseQueryOptions<unknown, Error> => {
-    return {
-        key: callWithDefaultParametersQueryKey(options),
-        query: async (context) => {
-            const { data } = await callWithDefaultParameters({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const callWithDefaultParametersQuery = defineQueryOptions((options?: Options<CallWithDefaultParametersData>) => ({
+    key: callWithDefaultParametersQueryKey(options),
+    query: async (context) => {
+        const { data } = await callWithDefaultParameters({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const callWithDefaultOptionalParametersMutation = (options?: Partial<Options<CallWithDefaultOptionalParametersData>>): UseMutationOptions<unknown, Options<CallWithDefaultOptionalParametersData>, Error> => {
     return {
@@ -375,19 +367,17 @@ export const duplicateNameMutation = (options?: Partial<Options<DuplicateNameDat
 
 export const duplicateName2QueryKey = (options?: Options<DuplicateName2Data>) => createQueryKey('duplicateName2', options);
 
-export const duplicateName2Query = (options?: Options<DuplicateName2Data>): UseQueryOptions<unknown, Error> => {
-    return {
-        key: duplicateName2QueryKey(options),
-        query: async (context) => {
-            const { data } = await duplicateName2({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const duplicateName2Query = defineQueryOptions((options?: Options<DuplicateName2Data>) => ({
+    key: duplicateName2QueryKey(options),
+    query: async (context) => {
+        const { data } = await duplicateName2({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const duplicateName3Mutation = (options?: Partial<Options<DuplicateName3Data>>): UseMutationOptions<unknown, Options<DuplicateName3Data>, Error> => {
     return {
@@ -417,83 +407,73 @@ export const duplicateName4Mutation = (options?: Partial<Options<DuplicateName4D
 
 export const callWithNoContentResponseQueryKey = (options?: Options<CallWithNoContentResponseData>) => createQueryKey('callWithNoContentResponse', options);
 
-export const callWithNoContentResponseQuery = (options?: Options<CallWithNoContentResponseData>): UseQueryOptions<CallWithNoContentResponseResponse, Error> => {
-    return {
-        key: callWithNoContentResponseQueryKey(options),
-        query: async (context) => {
-            const { data } = await callWithNoContentResponse({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const callWithNoContentResponseQuery = defineQueryOptions((options?: Options<CallWithNoContentResponseData>) => ({
+    key: callWithNoContentResponseQueryKey(options),
+    query: async (context) => {
+        const { data } = await callWithNoContentResponse({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const callWithResponseAndNoContentResponseQueryKey = (options?: Options<CallWithResponseAndNoContentResponseData>) => createQueryKey('callWithResponseAndNoContentResponse', options);
 
-export const callWithResponseAndNoContentResponseQuery = (options?: Options<CallWithResponseAndNoContentResponseData>): UseQueryOptions<CallWithResponseAndNoContentResponseResponse, Error> => {
-    return {
-        key: callWithResponseAndNoContentResponseQueryKey(options),
-        query: async (context) => {
-            const { data } = await callWithResponseAndNoContentResponse({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const callWithResponseAndNoContentResponseQuery = defineQueryOptions((options?: Options<CallWithResponseAndNoContentResponseData>) => ({
+    key: callWithResponseAndNoContentResponseQueryKey(options),
+    query: async (context) => {
+        const { data } = await callWithResponseAndNoContentResponse({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const dummyAQueryKey = (options?: Options<DummyAData>) => createQueryKey('dummyA', options);
 
-export const dummyAQuery = (options?: Options<DummyAData>): UseQueryOptions<DummyAResponse, Error> => {
-    return {
-        key: dummyAQueryKey(options),
-        query: async (context) => {
-            const { data } = await dummyA({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const dummyAQuery = defineQueryOptions((options?: Options<DummyAData>) => ({
+    key: dummyAQueryKey(options),
+    query: async (context) => {
+        const { data } = await dummyA({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const dummyBQueryKey = (options?: Options<DummyBData>) => createQueryKey('dummyB', options);
 
-export const dummyBQuery = (options?: Options<DummyBData>): UseQueryOptions<DummyBResponse, Error> => {
-    return {
-        key: dummyBQueryKey(options),
-        query: async (context) => {
-            const { data } = await dummyB({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const dummyBQuery = defineQueryOptions((options?: Options<DummyBData>) => ({
+    key: dummyBQueryKey(options),
+    query: async (context) => {
+        const { data } = await dummyB({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const callWithResponseQueryKey = (options?: Options<CallWithResponseData>) => createQueryKey('callWithResponse', options);
 
-export const callWithResponseQuery = (options?: Options<CallWithResponseData>): UseQueryOptions<CallWithResponseResponse, Error> => {
-    return {
-        key: callWithResponseQueryKey(options),
-        query: async (context) => {
-            const { data } = await callWithResponse({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const callWithResponseQuery = defineQueryOptions((options?: Options<CallWithResponseData>) => ({
+    key: callWithResponseQueryKey(options),
+    query: async (context) => {
+        const { data } = await callWithResponse({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const callWithDuplicateResponsesMutation = (options?: Partial<Options<CallWithDuplicateResponsesData>>): UseMutationOptions<CallWithDuplicateResponsesResponse, Options<CallWithDuplicateResponsesData>, CallWithDuplicateResponsesError> => {
     return {
@@ -523,35 +503,31 @@ export const callWithResponsesMutation = (options?: Partial<Options<CallWithResp
 
 export const collectionFormatQueryKey = (options: Options<CollectionFormatData>) => createQueryKey('collectionFormat', options);
 
-export const collectionFormatQuery = (options: Options<CollectionFormatData>): UseQueryOptions<unknown, Error> => {
-    return {
-        key: collectionFormatQueryKey(options),
-        query: async (context) => {
-            const { data } = await collectionFormat({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const collectionFormatQuery = defineQueryOptions((options: Options<CollectionFormatData>) => ({
+    key: collectionFormatQueryKey(options),
+    query: async (context) => {
+        const { data } = await collectionFormat({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const typesQueryKey = (options: Options<TypesData>) => createQueryKey('types', options);
 
-export const typesQuery = (options: Options<TypesData>): UseQueryOptions<TypesResponse, Error> => {
-    return {
-        key: typesQueryKey(options),
-        query: async (context) => {
-            const { data } = await types({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const typesQuery = defineQueryOptions((options: Options<TypesData>) => ({
+    key: typesQueryKey(options),
+    query: async (context) => {
+        const { data } = await types({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const uploadFileMutation = (options?: Partial<Options<UploadFileData>>): UseMutationOptions<UploadFileResponse, Options<UploadFileData>, Error> => {
     return {
@@ -568,51 +544,45 @@ export const uploadFileMutation = (options?: Partial<Options<UploadFileData>>):
 
 export const fileResponseQueryKey = (options: Options<FileResponseData>) => createQueryKey('fileResponse', options);
 
-export const fileResponseQuery = (options: Options<FileResponseData>): UseQueryOptions<FileResponseResponse, Error> => {
-    return {
-        key: fileResponseQueryKey(options),
-        query: async (context) => {
-            const { data } = await fileResponse({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const fileResponseQuery = defineQueryOptions((options: Options<FileResponseData>) => ({
+    key: fileResponseQueryKey(options),
+    query: async (context) => {
+        const { data } = await fileResponse({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const complexTypesQueryKey = (options: Options<ComplexTypesData>) => createQueryKey('complexTypes', options);
 
-export const complexTypesQuery = (options: Options<ComplexTypesData>): UseQueryOptions<ComplexTypesResponse, Error> => {
-    return {
-        key: complexTypesQueryKey(options),
-        query: async (context) => {
-            const { data } = await complexTypes({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const complexTypesQuery = defineQueryOptions((options: Options<ComplexTypesData>) => ({
+    key: complexTypesQueryKey(options),
+    query: async (context) => {
+        const { data } = await complexTypes({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const multipartResponseQueryKey = (options?: Options<MultipartResponseData>) => createQueryKey('multipartResponse', options);
 
-export const multipartResponseQuery = (options?: Options<MultipartResponseData>): UseQueryOptions<MultipartResponseResponse, Error> => {
-    return {
-        key: multipartResponseQueryKey(options),
-        query: async (context) => {
-            const { data } = await multipartResponse({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const multipartResponseQuery = defineQueryOptions((options?: Options<MultipartResponseData>) => ({
+    key: multipartResponseQueryKey(options),
+    query: async (context) => {
+        const { data } = await multipartResponse({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const multipartRequestMutation = (options?: Partial<Options<MultipartRequestData>>): UseMutationOptions<unknown, Options<MultipartRequestData>, Error> => {
     return {
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@pinia/colada/fetch/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@pinia/colada/fetch/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@pinia/colada/fetch/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@pinia/colada/fetch/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@pinia/colada/fetch/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@pinia/colada/fetch/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@pinia/colada/fetch/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/angular-query-experimental/asClass/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/angular-query-experimental/asClass/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/angular-query-experimental/asClass/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/angular-query-experimental/asClass/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/angular-query-experimental/asClass/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/angular-query-experimental/asClass/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/angular-query-experimental/asClass/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/angular-query-experimental/axios/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/angular-query-experimental/axios/client/index.ts
index 8ddc04f425..cff1d39c90 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/angular-query-experimental/axios/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/angular-query-experimental/axios/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/angular-query-experimental/axios/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/angular-query-experimental/axios/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/angular-query-experimental/axios/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/angular-query-experimental/fetch/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/angular-query-experimental/fetch/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/angular-query-experimental/fetch/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/angular-query-experimental/fetch/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/angular-query-experimental/fetch/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/angular-query-experimental/fetch/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/angular-query-experimental/fetch/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/angular-query-experimental/name-builder/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/angular-query-experimental/name-builder/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/angular-query-experimental/name-builder/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/angular-query-experimental/name-builder/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/angular-query-experimental/name-builder/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/angular-query-experimental/name-builder/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/angular-query-experimental/name-builder/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/react-query/asClass/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/react-query/asClass/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/react-query/asClass/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/react-query/asClass/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/react-query/asClass/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/react-query/asClass/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/react-query/asClass/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/react-query/axios/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/react-query/axios/client/index.ts
index 8ddc04f425..cff1d39c90 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/react-query/axios/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/react-query/axios/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/react-query/axios/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/react-query/axios/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/react-query/axios/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/react-query/fetch/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/react-query/fetch/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/react-query/fetch/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/react-query/fetch/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/react-query/fetch/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/react-query/fetch/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/react-query/fetch/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/react-query/name-builder/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/react-query/name-builder/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/react-query/name-builder/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/react-query/name-builder/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/react-query/name-builder/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/react-query/name-builder/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/react-query/name-builder/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/solid-query/asClass/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/solid-query/asClass/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/solid-query/asClass/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/solid-query/asClass/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/solid-query/asClass/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/solid-query/asClass/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/solid-query/asClass/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/solid-query/axios/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/solid-query/axios/client/index.ts
index 8ddc04f425..cff1d39c90 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/solid-query/axios/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/solid-query/axios/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/solid-query/axios/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/solid-query/axios/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/solid-query/axios/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/solid-query/fetch/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/solid-query/fetch/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/solid-query/fetch/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/solid-query/fetch/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/solid-query/fetch/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/solid-query/fetch/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/solid-query/fetch/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/solid-query/name-builder/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/solid-query/name-builder/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/solid-query/name-builder/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/solid-query/name-builder/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/solid-query/name-builder/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/solid-query/name-builder/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/solid-query/name-builder/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/svelte-query/asClass/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/svelte-query/asClass/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/svelte-query/asClass/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/svelte-query/asClass/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/svelte-query/asClass/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/svelte-query/asClass/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/svelte-query/asClass/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/svelte-query/axios/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/svelte-query/axios/client/index.ts
index 8ddc04f425..cff1d39c90 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/svelte-query/axios/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/svelte-query/axios/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/svelte-query/axios/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/svelte-query/axios/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/svelte-query/axios/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/svelte-query/fetch/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/svelte-query/fetch/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/svelte-query/fetch/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/svelte-query/fetch/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/svelte-query/fetch/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/svelte-query/fetch/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/svelte-query/fetch/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/svelte-query/name-builder/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/svelte-query/name-builder/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/svelte-query/name-builder/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/svelte-query/name-builder/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/svelte-query/name-builder/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/svelte-query/name-builder/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/svelte-query/name-builder/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/vue-query/asClass/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/vue-query/asClass/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/vue-query/asClass/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/vue-query/asClass/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/vue-query/asClass/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/vue-query/asClass/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/vue-query/asClass/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/vue-query/axios/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/vue-query/axios/client/index.ts
index 8ddc04f425..cff1d39c90 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/vue-query/axios/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/vue-query/axios/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/vue-query/axios/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/vue-query/axios/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/vue-query/axios/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/vue-query/fetch/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/vue-query/fetch/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/vue-query/fetch/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/vue-query/fetch/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/vue-query/fetch/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/vue-query/fetch/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/vue-query/fetch/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/vue-query/name-builder/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/vue-query/name-builder/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/vue-query/name-builder/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/vue-query/name-builder/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/vue-query/name-builder/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/vue-query/name-builder/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/vue-query/name-builder/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/security-api-key/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/security-api-key/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/security-api-key/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/security-api-key/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/security-api-key/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/security-api-key/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/security-api-key/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/security-false/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/security-false/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/security-false/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/security-false/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/security-false/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/security-false/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/security-false/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/security-http-bearer/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/security-http-bearer/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/security-http-bearer/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/security-http-bearer/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/security-http-bearer/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/security-http-bearer/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/security-http-bearer/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/security-oauth2/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/security-oauth2/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/security-oauth2/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/security-oauth2/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/security-oauth2/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/security-oauth2/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/security-oauth2/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/security-open-id-connect/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/security-open-id-connect/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/security-open-id-connect/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/security-open-id-connect/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/security-open-id-connect/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/security-open-id-connect/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/security-open-id-connect/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/servers/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/servers/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/servers/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/servers/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/servers/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/servers/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/servers/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/transformers-all-of/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/transformers-all-of/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/transformers-all-of/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/transformers-all-of/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/transformers-all-of/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/transformers-all-of/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/transformers-all-of/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/transformers-any-of-null/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/transformers-any-of-null/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/transformers-any-of-null/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/transformers-any-of-null/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/transformers-any-of-null/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/transformers-any-of-null/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/transformers-any-of-null/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/transformers-array/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/transformers-array/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/transformers-array/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/transformers-array/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/transformers-array/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/transformers-array/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/transformers-array/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/transforms-read-write/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/transforms-read-write/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/transforms-read-write/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/transforms-read-write/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/transforms-read-write/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/transforms-read-write/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/transforms-read-write/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/body-response-text-plain/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/body-response-text-plain/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/body-response-text-plain/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/body-response-text-plain/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/body-response-text-plain/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/body-response-text-plain/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/body-response-text-plain/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/base-url-false/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/base-url-false/client/index.ts
index 8ddc04f425..cff1d39c90 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/base-url-false/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/base-url-false/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/base-url-false/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/base-url-false/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/base-url-false/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/base-url-number/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/base-url-number/client/index.ts
index 8ddc04f425..cff1d39c90 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/base-url-number/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/base-url-number/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/base-url-number/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/base-url-number/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/base-url-number/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/base-url-strict/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/base-url-strict/client/index.ts
index 8ddc04f425..cff1d39c90 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/base-url-strict/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/base-url-strict/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/base-url-strict/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/base-url-strict/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/base-url-strict/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/base-url-string/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/base-url-string/client/index.ts
index 8ddc04f425..cff1d39c90 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/base-url-string/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/base-url-string/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/base-url-string/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/base-url-string/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/base-url-string/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/clean-false/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/clean-false/client/index.ts
index 8ddc04f425..cff1d39c90 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/clean-false/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/clean-false/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/clean-false/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/clean-false/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/clean-false/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/default/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/default/client/index.ts
index 8ddc04f425..cff1d39c90 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/default/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/default/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/default/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/default/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/default/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/sdk-client-optional/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/sdk-client-optional/client/index.ts
index 8ddc04f425..cff1d39c90 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/sdk-client-optional/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/sdk-client-optional/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/sdk-client-optional/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/sdk-client-optional/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/sdk-client-optional/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/sdk-client-required/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/sdk-client-required/client/index.ts
index 8ddc04f425..cff1d39c90 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/sdk-client-required/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/sdk-client-required/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/sdk-client-required/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/sdk-client-required/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/sdk-client-required/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/tsconfig-nodenext-sdk/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/tsconfig-nodenext-sdk/client/index.ts
index 771ff86c9e..f32aaa771d 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/tsconfig-nodenext-sdk/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/tsconfig-nodenext-sdk/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen.js';
 export { buildClientParams } from '../core/params.gen.js';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen.js';
 export { createClient } from './client.gen.js';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/tsconfig-nodenext-sdk/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/tsconfig-nodenext-sdk/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-axios/tsconfig-nodenext-sdk/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/base-url-false/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/base-url-false/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/base-url-false/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/base-url-false/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/base-url-false/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/base-url-false/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/base-url-false/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/base-url-number/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/base-url-number/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/base-url-number/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/base-url-number/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/base-url-number/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/base-url-number/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/base-url-number/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/base-url-strict/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/base-url-strict/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/base-url-strict/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/base-url-strict/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/base-url-strict/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/base-url-strict/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/base-url-strict/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/base-url-string/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/base-url-string/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/base-url-string/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/base-url-string/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/base-url-string/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/base-url-string/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/base-url-string/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/clean-false/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/clean-false/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/clean-false/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/clean-false/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/clean-false/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/clean-false/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/clean-false/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/default/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/default/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/default/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/default/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/default/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/default/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/default/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/sdk-client-optional/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/sdk-client-optional/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/sdk-client-optional/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/sdk-client-optional/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/sdk-client-optional/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/sdk-client-optional/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/sdk-client-optional/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/sdk-client-required/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/sdk-client-required/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/sdk-client-required/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/sdk-client-required/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/sdk-client-required/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/sdk-client-required/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/sdk-client-required/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/tsconfig-nodenext-sdk/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/tsconfig-nodenext-sdk/client/index.ts
index 99df3b8511..b4e8e87d0f 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/tsconfig-nodenext-sdk/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/tsconfig-nodenext-sdk/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen.js';
 export { buildClientParams } from '../core/params.gen.js';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen.js';
 export { createClient } from './client.gen.js';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/tsconfig-nodenext-sdk/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/tsconfig-nodenext-sdk/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-fetch/tsconfig-nodenext-sdk/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/base-url-false/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/base-url-false/client/index.ts
index 8ddc04f425..cff1d39c90 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/base-url-false/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/base-url-false/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/base-url-false/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/base-url-false/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/base-url-false/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/base-url-number/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/base-url-number/client/index.ts
index 8ddc04f425..cff1d39c90 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/base-url-number/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/base-url-number/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/base-url-number/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/base-url-number/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/base-url-number/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/base-url-strict/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/base-url-strict/client/index.ts
index 8ddc04f425..cff1d39c90 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/base-url-strict/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/base-url-strict/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/base-url-strict/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/base-url-strict/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/base-url-strict/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/base-url-string/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/base-url-string/client/index.ts
index 8ddc04f425..cff1d39c90 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/base-url-string/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/base-url-string/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/base-url-string/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/base-url-string/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/base-url-string/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/clean-false/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/clean-false/client/index.ts
index 8ddc04f425..cff1d39c90 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/clean-false/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/clean-false/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/clean-false/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/clean-false/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/clean-false/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/default/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/default/client/index.ts
index 8ddc04f425..cff1d39c90 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/default/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/default/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/default/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/default/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/default/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/sdk-client-optional/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/sdk-client-optional/client/index.ts
index 8ddc04f425..cff1d39c90 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/sdk-client-optional/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/sdk-client-optional/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/sdk-client-optional/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/sdk-client-optional/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/sdk-client-optional/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/sdk-client-required/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/sdk-client-required/client/index.ts
index 8ddc04f425..cff1d39c90 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/sdk-client-required/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/sdk-client-required/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/sdk-client-required/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/sdk-client-required/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/sdk-client-required/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/tsconfig-nodenext-sdk/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/tsconfig-nodenext-sdk/client/index.ts
index 771ff86c9e..f32aaa771d 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/tsconfig-nodenext-sdk/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/tsconfig-nodenext-sdk/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen.js';
 export { buildClientParams } from '../core/params.gen.js';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen.js';
 export { createClient } from './client.gen.js';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/tsconfig-nodenext-sdk/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/tsconfig-nodenext-sdk/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-next/tsconfig-nodenext-sdk/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/base-url-false/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/base-url-false/client/index.ts
index a2e8f2493f..f442748d17 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/base-url-false/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/base-url-false/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/base-url-false/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/base-url-false/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/base-url-false/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/base-url-number/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/base-url-number/client/index.ts
index a2e8f2493f..f442748d17 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/base-url-number/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/base-url-number/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/base-url-number/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/base-url-number/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/base-url-number/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/base-url-strict/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/base-url-strict/client/index.ts
index a2e8f2493f..f442748d17 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/base-url-strict/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/base-url-strict/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/base-url-strict/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/base-url-strict/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/base-url-strict/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/base-url-string/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/base-url-string/client/index.ts
index a2e8f2493f..f442748d17 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/base-url-string/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/base-url-string/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/base-url-string/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/base-url-string/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/base-url-string/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/clean-false/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/clean-false/client/index.ts
index a2e8f2493f..f442748d17 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/clean-false/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/clean-false/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/clean-false/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/clean-false/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/clean-false/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/default/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/default/client/index.ts
index a2e8f2493f..f442748d17 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/default/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/default/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/default/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/default/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/default/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/sdk-client-optional/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/sdk-client-optional/client/index.ts
index a2e8f2493f..f442748d17 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/sdk-client-optional/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/sdk-client-optional/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/sdk-client-optional/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/sdk-client-optional/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/sdk-client-optional/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/sdk-client-required/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/sdk-client-required/client/index.ts
index a2e8f2493f..f442748d17 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/sdk-client-required/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/sdk-client-required/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/sdk-client-required/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/sdk-client-required/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/sdk-client-required/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/tsconfig-nodenext-sdk/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/tsconfig-nodenext-sdk/client/index.ts
index 8bfc39df07..cbc00f0f6c 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/tsconfig-nodenext-sdk/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/tsconfig-nodenext-sdk/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen.js';
 export { buildClientParams } from '../core/params.gen.js';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen.js';
 export { createClient } from './client.gen.js';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/tsconfig-nodenext-sdk/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/tsconfig-nodenext-sdk/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-nuxt/tsconfig-nodenext-sdk/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/base-url-false/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/base-url-false/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/base-url-false/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/base-url-false/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/base-url-false/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/base-url-false/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/base-url-false/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/base-url-number/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/base-url-number/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/base-url-number/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/base-url-number/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/base-url-number/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/base-url-number/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/base-url-number/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/base-url-strict/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/base-url-strict/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/base-url-strict/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/base-url-strict/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/base-url-strict/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/base-url-strict/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/base-url-strict/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/base-url-string/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/base-url-string/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/base-url-string/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/base-url-string/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/base-url-string/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/base-url-string/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/base-url-string/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/clean-false/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/clean-false/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/clean-false/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/clean-false/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/clean-false/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/clean-false/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/clean-false/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/default/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/default/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/default/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/default/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/default/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/default/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/default/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/sdk-client-optional/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/sdk-client-optional/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/sdk-client-optional/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/sdk-client-optional/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/sdk-client-optional/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/sdk-client-optional/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/sdk-client-optional/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/sdk-client-required/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/sdk-client-required/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/sdk-client-required/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/sdk-client-required/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/sdk-client-required/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/sdk-client-required/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/sdk-client-required/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/tsconfig-nodenext-sdk/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/tsconfig-nodenext-sdk/client/index.ts
index 99df3b8511..b4e8e87d0f 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/tsconfig-nodenext-sdk/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/tsconfig-nodenext-sdk/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen.js';
 export { buildClientParams } from '../core/params.gen.js';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen.js';
 export { createClient } from './client.gen.js';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/tsconfig-nodenext-sdk/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/tsconfig-nodenext-sdk/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/clients/@hey-api/client-ofetch/tsconfig-nodenext-sdk/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/content-types/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/content-types/client/index.ts
index 8ddc04f425..cff1d39c90 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/content-types/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/content-types/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/content-types/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/content-types/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/content-types/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/headers/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/headers/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/headers/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/headers/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/headers/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/headers/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/headers/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/internal-name-conflict/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/internal-name-conflict/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/internal-name-conflict/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/internal-name-conflict/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/internal-name-conflict/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/internal-name-conflict/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/internal-name-conflict/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/pagination-ref/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/pagination-ref/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/pagination-ref/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/pagination-ref/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/pagination-ref/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/pagination-ref/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/pagination-ref/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/parameter-explode-false-axios/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/parameter-explode-false-axios/client/index.ts
index 8ddc04f425..cff1d39c90 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/parameter-explode-false-axios/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/parameter-explode-false-axios/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/parameter-explode-false-axios/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/parameter-explode-false-axios/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/parameter-explode-false-axios/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/parameter-explode-false/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/parameter-explode-false/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/parameter-explode-false/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/parameter-explode-false/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/parameter-explode-false/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/parameter-explode-false/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/parameter-explode-false/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@angular/common/default-class/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@angular/common/default-class/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@angular/common/default-class/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@angular/common/default-class/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@angular/common/default-class/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@angular/common/default-class/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@angular/common/default-class/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@angular/common/default/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@angular/common/default/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@angular/common/default/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@angular/common/default/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@angular/common/default/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@angular/common/default/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@angular/common/default/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/client-fetch/sdk-nested-classes-instance/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/client-fetch/sdk-nested-classes-instance/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/client-fetch/sdk-nested-classes-instance/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/client-fetch/sdk-nested-classes-instance/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/client-fetch/sdk-nested-classes-instance/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/client-fetch/sdk-nested-classes-instance/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/client-fetch/sdk-nested-classes-instance/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/client-fetch/sdk-nested-classes/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/client-fetch/sdk-nested-classes/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/client-fetch/sdk-nested-classes/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/client-fetch/sdk-nested-classes/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/client-fetch/sdk-nested-classes/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/client-fetch/sdk-nested-classes/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/client-fetch/sdk-nested-classes/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/sdk/default/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/sdk/default/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/sdk/default/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/sdk/default/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/sdk/default/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/sdk/default/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/sdk/default/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/sdk/instance/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/sdk/instance/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/sdk/instance/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/sdk/instance/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/sdk/instance/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/sdk/instance/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/sdk/instance/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/sdk/throwOnError/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/sdk/throwOnError/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/sdk/throwOnError/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/sdk/throwOnError/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/sdk/throwOnError/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/sdk/throwOnError/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/sdk/throwOnError/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/transformers/type-format-valibot/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/transformers/type-format-valibot/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/transformers/type-format-valibot/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/transformers/type-format-valibot/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/transformers/type-format-valibot/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/transformers/type-format-valibot/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/transformers/type-format-valibot/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/transformers/type-format-zod/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/transformers/type-format-zod/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/transformers/type-format-zod/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/transformers/type-format-zod/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/transformers/type-format-zod/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/transformers/type-format-zod/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/transformers/type-format-zod/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/typescript/transforms-read-write-custom-name/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/typescript/transforms-read-write-custom-name/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/typescript/transforms-read-write-custom-name/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/typescript/transforms-read-write-custom-name/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/typescript/transforms-read-write-custom-name/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/typescript/transforms-read-write-custom-name/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/typescript/transforms-read-write-custom-name/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/typescript/transforms-read-write-ignore/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/typescript/transforms-read-write-ignore/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/typescript/transforms-read-write-ignore/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/typescript/transforms-read-write-ignore/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/typescript/transforms-read-write-ignore/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/typescript/transforms-read-write-ignore/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@hey-api/typescript/transforms-read-write-ignore/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@pinia/colada/asClass/@pinia/colada.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@pinia/colada/asClass/@pinia/colada.gen.ts
index a8d9f65a68..1d845eca9b 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@pinia/colada/asClass/@pinia/colada.gen.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@pinia/colada/asClass/@pinia/colada.gen.ts
@@ -1,16 +1,17 @@
 // This file is auto-generated by @hey-api/openapi-ts
 
-import type { _JSONValue, UseMutationOptions, UseQueryOptions } from '@pinia/colada';
+import { type _JSONValue, defineQueryOptions, type UseMutationOptions } from '@pinia/colada';
 
+import { serializeQueryKeyValue } from '../client';
 import { client } from '../client.gen';
 import { BarBazService, FooBazService, type Options } from '../sdk.gen';
-import type { FooBarPostData, FooBarPostResponse, FooBarPutData, FooBarPutResponse, FooPostData, FooPostResponse, FooPutData, FooPutResponse, GetFooBarData, GetFooBarResponse, GetFooData, GetFooResponse } from '../types.gen';
+import type { FooBarPostData, FooBarPostResponse, FooBarPutData, FooBarPutResponse, FooPostData, FooPostResponse, FooPutData, FooPutResponse, GetFooBarData, GetFooData } from '../types.gen';
 
 export type QueryKey<TOptions extends Options> = [
-    Pick<TOptions, 'body' | 'path'> & {
+    Pick<TOptions, 'path'> & {
         _id: string;
         baseUrl?: _JSONValue;
-        headers?: _JSONValue;
+        body?: _JSONValue;
         query?: _JSONValue;
         tags?: _JSONValue;
     }
@@ -21,19 +22,22 @@ const createQueryKey = <TOptions extends Options>(id: string, options?: TOptions
 ] => {
     const params: QueryKey<TOptions>[0] = { _id: id, baseUrl: options?.baseUrl || (options?.client ?? client).getConfig().baseUrl } as QueryKey<TOptions>[0];
     if (tags) {
-        params.tags = tags as unknown as undefined;
+        params.tags = tags as unknown as _JSONValue;
     }
-    if (options?.body) {
-        params.body = options.body;
-    }
-    if (options?.headers) {
-        params.headers = options.headers as unknown as undefined;
+    if (options?.body !== undefined) {
+        const normalizedBody = serializeQueryKeyValue(options.body);
+        if (normalizedBody !== undefined) {
+            params.body = normalizedBody;
+        }
     }
     if (options?.path) {
         params.path = options.path;
     }
-    if (options?.query) {
-        params.query = options.query as unknown as undefined;
+    if (options?.query !== undefined) {
+        const normalizedQuery = serializeQueryKeyValue(options.query);
+        if (normalizedQuery !== undefined) {
+            params.query = normalizedQuery;
+        }
     }
     return [
         params
@@ -42,19 +46,17 @@ const createQueryKey = <TOptions extends Options>(id: string, options?: TOptions
 
 export const getFooQueryKey = (options?: Options<GetFooData>) => createQueryKey('getFoo', options);
 
-export const getFooQuery = (options?: Options<GetFooData>): UseQueryOptions<GetFooResponse, Error> => {
-    return {
-        key: getFooQueryKey(options),
-        query: async (context) => {
-            const { data } = await FooBazService.getFoo({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const getFooQuery = defineQueryOptions((options?: Options<GetFooData>) => ({
+    key: getFooQueryKey(options),
+    query: async (context) => {
+        const { data } = await FooBazService.getFoo({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const fooPostMutation = (options?: Partial<Options<FooPostData>>): UseMutationOptions<FooPostResponse, Options<FooPostData>, Error> => {
     return {
@@ -84,19 +86,17 @@ export const fooPutMutation = (options?: Partial<Options<FooPutData>>): UseMutat
 
 export const getFooBarQueryKey = (options?: Options<GetFooBarData>) => createQueryKey('getFooBar', options);
 
-export const getFooBarQuery = (options?: Options<GetFooBarData>): UseQueryOptions<GetFooBarResponse, Error> => {
-    return {
-        key: getFooBarQueryKey(options),
-        query: async (context) => {
-            const { data } = await BarBazService.getFooBar({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const getFooBarQuery = defineQueryOptions((options?: Options<GetFooBarData>) => ({
+    key: getFooBarQueryKey(options),
+    query: async (context) => {
+        const { data } = await BarBazService.getFooBar({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const fooBarPostMutation = (options?: Partial<Options<FooBarPostData>>): UseMutationOptions<FooBarPostResponse, Options<FooBarPostData>, Error> => {
     return {
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@pinia/colada/asClass/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@pinia/colada/asClass/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@pinia/colada/asClass/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@pinia/colada/asClass/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@pinia/colada/asClass/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@pinia/colada/asClass/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@pinia/colada/asClass/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@pinia/colada/fetch/@pinia/colada.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@pinia/colada/fetch/@pinia/colada.gen.ts
index 593b8e81ab..5f822ac96f 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@pinia/colada/fetch/@pinia/colada.gen.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@pinia/colada/fetch/@pinia/colada.gen.ts
@@ -1,16 +1,17 @@
 // This file is auto-generated by @hey-api/openapi-ts
 
-import type { _JSONValue, UseMutationOptions, UseQueryOptions } from '@pinia/colada';
+import { type _JSONValue, defineQueryOptions, type UseMutationOptions } from '@pinia/colada';
 
+import { serializeQueryKeyValue } from '../client';
 import { client } from '../client.gen';
 import { apiVVersionODataControllerCount, callToTestOrderOfParams, callWithDefaultOptionalParameters, callWithDefaultParameters, callWithDescriptions, callWithDuplicateResponses, callWithNoContentResponse, callWithParameters, callWithResponse, callWithResponseAndNoContentResponse, callWithResponses, callWithResultFromHeader, callWithWeirdParameterNames, collectionFormat, complexParams, complexTypes, deleteCallWithoutParametersAndResponse, deleteFoo, deprecatedCall, dummyA, dummyB, duplicateName, duplicateName2, duplicateName3, duplicateName4, export_, fileResponse, fooWow, getApiVbyApiVersionSimpleOperation, getCallWithOptionalParam, getCallWithoutParametersAndResponse, import_, multipartRequest, multipartResponse, nonAsciiæøåÆøÅöôêÊ字符串, type Options, patchApiVbyApiVersionNoTag, patchCallWithoutParametersAndResponse, postApiVbyApiVersionFormData, postApiVbyApiVersionRequestBody, postCallWithOptionalParam, postCallWithoutParametersAndResponse, putCallWithoutParametersAndResponse, putWithFormUrlEncoded, testErrorCode, types, uploadFile } from '../sdk.gen';
-import type { ApiVVersionODataControllerCountData, ApiVVersionODataControllerCountResponse, CallToTestOrderOfParamsData, CallWithDefaultOptionalParametersData, CallWithDefaultParametersData, CallWithDescriptionsData, CallWithDuplicateResponsesData, CallWithDuplicateResponsesError, CallWithDuplicateResponsesResponse, CallWithNoContentResponseData, CallWithNoContentResponseResponse, CallWithParametersData, CallWithResponseAndNoContentResponseData, CallWithResponseAndNoContentResponseResponse, CallWithResponseData, CallWithResponseResponse, CallWithResponsesData, CallWithResponsesError, CallWithResponsesResponse, CallWithResultFromHeaderData, CallWithWeirdParameterNamesData, CollectionFormatData, ComplexParamsData, ComplexParamsResponse, ComplexTypesData, ComplexTypesResponse, DeleteCallWithoutParametersAndResponseData, DeleteFooData3, DeprecatedCallData, DummyAData, DummyAResponse, DummyBData, DummyBResponse, DuplicateName2Data, DuplicateName3Data, DuplicateName4Data, DuplicateNameData, ExportData, FileResponseData, FileResponseResponse, FooWowData, GetApiVbyApiVersionSimpleOperationData, GetApiVbyApiVersionSimpleOperationError, GetApiVbyApiVersionSimpleOperationResponse, GetCallWithOptionalParamData, GetCallWithoutParametersAndResponseData, ImportData, ImportResponse, MultipartRequestData, MultipartResponseData, MultipartResponseResponse, NonAsciiæøåÆøÅöôêÊ字符串Data, NonAsciiæøåÆøÅöôêÊ字符串Response, PatchApiVbyApiVersionNoTagData, PatchCallWithoutParametersAndResponseData, PostApiVbyApiVersionFormDataData, PostApiVbyApiVersionRequestBodyData, PostCallWithOptionalParamData, PostCallWithOptionalParamResponse, PostCallWithoutParametersAndResponseData, PutCallWithoutParametersAndResponseData, PutWithFormUrlEncodedData, TestErrorCodeData, TypesData, TypesResponse, UploadFileData, UploadFileResponse } from '../types.gen';
+import type { ApiVVersionODataControllerCountData, CallToTestOrderOfParamsData, CallWithDefaultOptionalParametersData, CallWithDefaultParametersData, CallWithDescriptionsData, CallWithDuplicateResponsesData, CallWithDuplicateResponsesError, CallWithDuplicateResponsesResponse, CallWithNoContentResponseData, CallWithParametersData, CallWithResponseAndNoContentResponseData, CallWithResponseData, CallWithResponsesData, CallWithResponsesError, CallWithResponsesResponse, CallWithResultFromHeaderData, CallWithWeirdParameterNamesData, CollectionFormatData, ComplexParamsData, ComplexParamsResponse, ComplexTypesData, DeleteCallWithoutParametersAndResponseData, DeleteFooData3, DeprecatedCallData, DummyAData, DummyBData, DuplicateName2Data, DuplicateName3Data, DuplicateName4Data, DuplicateNameData, ExportData, FileResponseData, FooWowData, GetApiVbyApiVersionSimpleOperationData, GetCallWithOptionalParamData, GetCallWithoutParametersAndResponseData, ImportData, ImportResponse, MultipartRequestData, MultipartResponseData, NonAsciiæøåÆøÅöôêÊ字符串Data, NonAsciiæøåÆøÅöôêÊ字符串Response, PatchApiVbyApiVersionNoTagData, PatchCallWithoutParametersAndResponseData, PostApiVbyApiVersionFormDataData, PostApiVbyApiVersionRequestBodyData, PostCallWithOptionalParamData, PostCallWithOptionalParamResponse, PostCallWithoutParametersAndResponseData, PutCallWithoutParametersAndResponseData, PutWithFormUrlEncodedData, TestErrorCodeData, TypesData, UploadFileData, UploadFileResponse } from '../types.gen';
 
 export type QueryKey<TOptions extends Options> = [
-    Pick<TOptions, 'body' | 'path'> & {
+    Pick<TOptions, 'path'> & {
         _id: string;
         baseUrl?: _JSONValue;
-        headers?: _JSONValue;
+        body?: _JSONValue;
         query?: _JSONValue;
         tags?: _JSONValue;
     }
@@ -21,19 +22,22 @@ const createQueryKey = <TOptions extends Options>(id: string, options?: TOptions
 ] => {
     const params: QueryKey<TOptions>[0] = { _id: id, baseUrl: options?.baseUrl || (options?.client ?? client).getConfig().baseUrl } as QueryKey<TOptions>[0];
     if (tags) {
-        params.tags = tags as unknown as undefined;
+        params.tags = tags as unknown as _JSONValue;
     }
-    if (options?.body) {
-        params.body = options.body;
-    }
-    if (options?.headers) {
-        params.headers = options.headers as unknown as undefined;
+    if (options?.body !== undefined) {
+        const normalizedBody = serializeQueryKeyValue(options.body);
+        if (normalizedBody !== undefined) {
+            params.body = normalizedBody;
+        }
     }
     if (options?.path) {
         params.path = options.path;
     }
-    if (options?.query) {
-        params.query = options.query as unknown as undefined;
+    if (options?.query !== undefined) {
+        const normalizedQuery = serializeQueryKeyValue(options.query);
+        if (normalizedQuery !== undefined) {
+            params.query = normalizedQuery;
+        }
     }
     return [
         params
@@ -42,19 +46,17 @@ const createQueryKey = <TOptions extends Options>(id: string, options?: TOptions
 
 export const exportQueryKey = (options?: Options<ExportData>) => createQueryKey('export', options);
 
-export const exportQuery = (options?: Options<ExportData>): UseQueryOptions<unknown, Error> => {
-    return {
-        key: exportQueryKey(options),
-        query: async (context) => {
-            const { data } = await export_({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const exportQuery = defineQueryOptions((options?: Options<ExportData>) => ({
+    key: exportQueryKey(options),
+    query: async (context) => {
+        const { data } = await export_({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const patchApiVbyApiVersionNoTagMutation = (options?: Partial<Options<PatchApiVbyApiVersionNoTagData>>): UseMutationOptions<unknown, Options<PatchApiVbyApiVersionNoTagData>, Error> => {
     return {
@@ -97,35 +99,31 @@ export const fooWowMutation = (options?: Partial<Options<FooWowData>>): UseMutat
 
 export const apiVVersionODataControllerCountQueryKey = (options?: Options<ApiVVersionODataControllerCountData>) => createQueryKey('apiVVersionODataControllerCount', options);
 
-export const apiVVersionODataControllerCountQuery = (options?: Options<ApiVVersionODataControllerCountData>): UseQueryOptions<ApiVVersionODataControllerCountResponse, Error> => {
-    return {
-        key: apiVVersionODataControllerCountQueryKey(options),
-        query: async (context) => {
-            const { data } = await apiVVersionODataControllerCount({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const apiVVersionODataControllerCountQuery = defineQueryOptions((options?: Options<ApiVVersionODataControllerCountData>) => ({
+    key: apiVVersionODataControllerCountQueryKey(options),
+    query: async (context) => {
+        const { data } = await apiVVersionODataControllerCount({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const getApiVbyApiVersionSimpleOperationQueryKey = (options: Options<GetApiVbyApiVersionSimpleOperationData>) => createQueryKey('getApiVbyApiVersionSimpleOperation', options);
 
-export const getApiVbyApiVersionSimpleOperationQuery = (options: Options<GetApiVbyApiVersionSimpleOperationData>): UseQueryOptions<GetApiVbyApiVersionSimpleOperationResponse, GetApiVbyApiVersionSimpleOperationError> => {
-    return {
-        key: getApiVbyApiVersionSimpleOperationQueryKey(options),
-        query: async (context) => {
-            const { data } = await getApiVbyApiVersionSimpleOperation({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const getApiVbyApiVersionSimpleOperationQuery = defineQueryOptions((options: Options<GetApiVbyApiVersionSimpleOperationData>) => ({
+    key: getApiVbyApiVersionSimpleOperationQueryKey(options),
+    query: async (context) => {
+        const { data } = await getApiVbyApiVersionSimpleOperation({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const deleteCallWithoutParametersAndResponseMutation = (options?: Partial<Options<DeleteCallWithoutParametersAndResponseData>>): UseMutationOptions<unknown, Options<DeleteCallWithoutParametersAndResponseData>, Error> => {
     return {
@@ -142,19 +140,17 @@ export const deleteCallWithoutParametersAndResponseMutation = (options?: Partial
 
 export const getCallWithoutParametersAndResponseQueryKey = (options?: Options<GetCallWithoutParametersAndResponseData>) => createQueryKey('getCallWithoutParametersAndResponse', options);
 
-export const getCallWithoutParametersAndResponseQuery = (options?: Options<GetCallWithoutParametersAndResponseData>): UseQueryOptions<unknown, Error> => {
-    return {
-        key: getCallWithoutParametersAndResponseQueryKey(options),
-        query: async (context) => {
-            const { data } = await getCallWithoutParametersAndResponse({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const getCallWithoutParametersAndResponseQuery = defineQueryOptions((options?: Options<GetCallWithoutParametersAndResponseData>) => ({
+    key: getCallWithoutParametersAndResponseQueryKey(options),
+    query: async (context) => {
+        const { data } = await getCallWithoutParametersAndResponse({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const patchCallWithoutParametersAndResponseMutation = (options?: Partial<Options<PatchCallWithoutParametersAndResponseData>>): UseMutationOptions<unknown, Options<PatchCallWithoutParametersAndResponseData>, Error> => {
     return {
@@ -265,19 +261,17 @@ export const callWithWeirdParameterNamesMutation = (options?: Partial<Options<Ca
 
 export const getCallWithOptionalParamQueryKey = (options: Options<GetCallWithOptionalParamData>) => createQueryKey('getCallWithOptionalParam', options);
 
-export const getCallWithOptionalParamQuery = (options: Options<GetCallWithOptionalParamData>): UseQueryOptions<unknown, Error> => {
-    return {
-        key: getCallWithOptionalParamQueryKey(options),
-        query: async (context) => {
-            const { data } = await getCallWithOptionalParam({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const getCallWithOptionalParamQuery = defineQueryOptions((options: Options<GetCallWithOptionalParamData>) => ({
+    key: getCallWithOptionalParamQueryKey(options),
+    query: async (context) => {
+        const { data } = await getCallWithOptionalParam({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const postCallWithOptionalParamMutation = (options?: Partial<Options<PostCallWithOptionalParamData>>): UseMutationOptions<PostCallWithOptionalParamResponse, Options<PostCallWithOptionalParamData>, Error> => {
     return {
@@ -320,19 +314,17 @@ export const postApiVbyApiVersionFormDataMutation = (options?: Partial<Options<P
 
 export const callWithDefaultParametersQueryKey = (options?: Options<CallWithDefaultParametersData>) => createQueryKey('callWithDefaultParameters', options);
 
-export const callWithDefaultParametersQuery = (options?: Options<CallWithDefaultParametersData>): UseQueryOptions<unknown, Error> => {
-    return {
-        key: callWithDefaultParametersQueryKey(options),
-        query: async (context) => {
-            const { data } = await callWithDefaultParameters({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const callWithDefaultParametersQuery = defineQueryOptions((options?: Options<CallWithDefaultParametersData>) => ({
+    key: callWithDefaultParametersQueryKey(options),
+    query: async (context) => {
+        const { data } = await callWithDefaultParameters({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const callWithDefaultOptionalParametersMutation = (options?: Partial<Options<CallWithDefaultOptionalParametersData>>): UseMutationOptions<unknown, Options<CallWithDefaultOptionalParametersData>, Error> => {
     return {
@@ -375,19 +367,17 @@ export const duplicateNameMutation = (options?: Partial<Options<DuplicateNameDat
 
 export const duplicateName2QueryKey = (options?: Options<DuplicateName2Data>) => createQueryKey('duplicateName2', options);
 
-export const duplicateName2Query = (options?: Options<DuplicateName2Data>): UseQueryOptions<unknown, Error> => {
-    return {
-        key: duplicateName2QueryKey(options),
-        query: async (context) => {
-            const { data } = await duplicateName2({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const duplicateName2Query = defineQueryOptions((options?: Options<DuplicateName2Data>) => ({
+    key: duplicateName2QueryKey(options),
+    query: async (context) => {
+        const { data } = await duplicateName2({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const duplicateName3Mutation = (options?: Partial<Options<DuplicateName3Data>>): UseMutationOptions<unknown, Options<DuplicateName3Data>, Error> => {
     return {
@@ -417,83 +407,73 @@ export const duplicateName4Mutation = (options?: Partial<Options<DuplicateName4D
 
 export const callWithNoContentResponseQueryKey = (options?: Options<CallWithNoContentResponseData>) => createQueryKey('callWithNoContentResponse', options);
 
-export const callWithNoContentResponseQuery = (options?: Options<CallWithNoContentResponseData>): UseQueryOptions<CallWithNoContentResponseResponse, Error> => {
-    return {
-        key: callWithNoContentResponseQueryKey(options),
-        query: async (context) => {
-            const { data } = await callWithNoContentResponse({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const callWithNoContentResponseQuery = defineQueryOptions((options?: Options<CallWithNoContentResponseData>) => ({
+    key: callWithNoContentResponseQueryKey(options),
+    query: async (context) => {
+        const { data } = await callWithNoContentResponse({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const callWithResponseAndNoContentResponseQueryKey = (options?: Options<CallWithResponseAndNoContentResponseData>) => createQueryKey('callWithResponseAndNoContentResponse', options);
 
-export const callWithResponseAndNoContentResponseQuery = (options?: Options<CallWithResponseAndNoContentResponseData>): UseQueryOptions<CallWithResponseAndNoContentResponseResponse, Error> => {
-    return {
-        key: callWithResponseAndNoContentResponseQueryKey(options),
-        query: async (context) => {
-            const { data } = await callWithResponseAndNoContentResponse({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const callWithResponseAndNoContentResponseQuery = defineQueryOptions((options?: Options<CallWithResponseAndNoContentResponseData>) => ({
+    key: callWithResponseAndNoContentResponseQueryKey(options),
+    query: async (context) => {
+        const { data } = await callWithResponseAndNoContentResponse({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const dummyAQueryKey = (options?: Options<DummyAData>) => createQueryKey('dummyA', options);
 
-export const dummyAQuery = (options?: Options<DummyAData>): UseQueryOptions<DummyAResponse, Error> => {
-    return {
-        key: dummyAQueryKey(options),
-        query: async (context) => {
-            const { data } = await dummyA({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const dummyAQuery = defineQueryOptions((options?: Options<DummyAData>) => ({
+    key: dummyAQueryKey(options),
+    query: async (context) => {
+        const { data } = await dummyA({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const dummyBQueryKey = (options?: Options<DummyBData>) => createQueryKey('dummyB', options);
 
-export const dummyBQuery = (options?: Options<DummyBData>): UseQueryOptions<DummyBResponse, Error> => {
-    return {
-        key: dummyBQueryKey(options),
-        query: async (context) => {
-            const { data } = await dummyB({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const dummyBQuery = defineQueryOptions((options?: Options<DummyBData>) => ({
+    key: dummyBQueryKey(options),
+    query: async (context) => {
+        const { data } = await dummyB({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const callWithResponseQueryKey = (options?: Options<CallWithResponseData>) => createQueryKey('callWithResponse', options);
 
-export const callWithResponseQuery = (options?: Options<CallWithResponseData>): UseQueryOptions<CallWithResponseResponse, Error> => {
-    return {
-        key: callWithResponseQueryKey(options),
-        query: async (context) => {
-            const { data } = await callWithResponse({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const callWithResponseQuery = defineQueryOptions((options?: Options<CallWithResponseData>) => ({
+    key: callWithResponseQueryKey(options),
+    query: async (context) => {
+        const { data } = await callWithResponse({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const callWithDuplicateResponsesMutation = (options?: Partial<Options<CallWithDuplicateResponsesData>>): UseMutationOptions<CallWithDuplicateResponsesResponse, Options<CallWithDuplicateResponsesData>, CallWithDuplicateResponsesError> => {
     return {
@@ -523,35 +503,31 @@ export const callWithResponsesMutation = (options?: Partial<Options<CallWithResp
 
 export const collectionFormatQueryKey = (options: Options<CollectionFormatData>) => createQueryKey('collectionFormat', options);
 
-export const collectionFormatQuery = (options: Options<CollectionFormatData>): UseQueryOptions<unknown, Error> => {
-    return {
-        key: collectionFormatQueryKey(options),
-        query: async (context) => {
-            const { data } = await collectionFormat({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const collectionFormatQuery = defineQueryOptions((options: Options<CollectionFormatData>) => ({
+    key: collectionFormatQueryKey(options),
+    query: async (context) => {
+        const { data } = await collectionFormat({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const typesQueryKey = (options: Options<TypesData>) => createQueryKey('types', options);
 
-export const typesQuery = (options: Options<TypesData>): UseQueryOptions<TypesResponse, Error> => {
-    return {
-        key: typesQueryKey(options),
-        query: async (context) => {
-            const { data } = await types({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const typesQuery = defineQueryOptions((options: Options<TypesData>) => ({
+    key: typesQueryKey(options),
+    query: async (context) => {
+        const { data } = await types({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const uploadFileMutation = (options?: Partial<Options<UploadFileData>>): UseMutationOptions<UploadFileResponse, Options<UploadFileData>, Error> => {
     return {
@@ -568,51 +544,45 @@ export const uploadFileMutation = (options?: Partial<Options<UploadFileData>>):
 
 export const fileResponseQueryKey = (options: Options<FileResponseData>) => createQueryKey('fileResponse', options);
 
-export const fileResponseQuery = (options: Options<FileResponseData>): UseQueryOptions<FileResponseResponse, Error> => {
-    return {
-        key: fileResponseQueryKey(options),
-        query: async (context) => {
-            const { data } = await fileResponse({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const fileResponseQuery = defineQueryOptions((options: Options<FileResponseData>) => ({
+    key: fileResponseQueryKey(options),
+    query: async (context) => {
+        const { data } = await fileResponse({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const complexTypesQueryKey = (options: Options<ComplexTypesData>) => createQueryKey('complexTypes', options);
 
-export const complexTypesQuery = (options: Options<ComplexTypesData>): UseQueryOptions<ComplexTypesResponse, Error> => {
-    return {
-        key: complexTypesQueryKey(options),
-        query: async (context) => {
-            const { data } = await complexTypes({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const complexTypesQuery = defineQueryOptions((options: Options<ComplexTypesData>) => ({
+    key: complexTypesQueryKey(options),
+    query: async (context) => {
+        const { data } = await complexTypes({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const multipartResponseQueryKey = (options?: Options<MultipartResponseData>) => createQueryKey('multipartResponse', options);
 
-export const multipartResponseQuery = (options?: Options<MultipartResponseData>): UseQueryOptions<MultipartResponseResponse, Error> => {
-    return {
-        key: multipartResponseQueryKey(options),
-        query: async (context) => {
-            const { data } = await multipartResponse({
-                ...options,
-                ...context,
-                throwOnError: true
-            });
-            return data;
-        }
-    };
-};
+export const multipartResponseQuery = defineQueryOptions((options?: Options<MultipartResponseData>) => ({
+    key: multipartResponseQueryKey(options),
+    query: async (context) => {
+        const { data } = await multipartResponse({
+            ...options,
+            ...context,
+            throwOnError: true
+        });
+        return data;
+    }
+}));
 
 export const multipartRequestMutation = (options?: Partial<Options<MultipartRequestData>>): UseMutationOptions<unknown, Options<MultipartRequestData>, Error> => {
     return {
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@pinia/colada/fetch/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@pinia/colada/fetch/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@pinia/colada/fetch/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@pinia/colada/fetch/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@pinia/colada/fetch/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@pinia/colada/fetch/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@pinia/colada/fetch/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/angular-query-experimental/asClass/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/angular-query-experimental/asClass/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/angular-query-experimental/asClass/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/angular-query-experimental/asClass/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/angular-query-experimental/asClass/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/angular-query-experimental/asClass/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/angular-query-experimental/asClass/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/angular-query-experimental/axios/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/angular-query-experimental/axios/client/index.ts
index 8ddc04f425..cff1d39c90 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/angular-query-experimental/axios/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/angular-query-experimental/axios/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/angular-query-experimental/axios/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/angular-query-experimental/axios/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/angular-query-experimental/axios/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/angular-query-experimental/fetch/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/angular-query-experimental/fetch/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/angular-query-experimental/fetch/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/angular-query-experimental/fetch/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/angular-query-experimental/fetch/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/angular-query-experimental/fetch/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/angular-query-experimental/fetch/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/angular-query-experimental/name-builder/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/angular-query-experimental/name-builder/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/angular-query-experimental/name-builder/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/angular-query-experimental/name-builder/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/angular-query-experimental/name-builder/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/angular-query-experimental/name-builder/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/angular-query-experimental/name-builder/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/react-query/asClass/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/react-query/asClass/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/react-query/asClass/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/react-query/asClass/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/react-query/asClass/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/react-query/asClass/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/react-query/asClass/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/react-query/axios/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/react-query/axios/client/index.ts
index 8ddc04f425..cff1d39c90 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/react-query/axios/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/react-query/axios/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/react-query/axios/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/react-query/axios/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/react-query/axios/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/react-query/fetch/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/react-query/fetch/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/react-query/fetch/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/react-query/fetch/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/react-query/fetch/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/react-query/fetch/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/react-query/fetch/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/react-query/name-builder/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/react-query/name-builder/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/react-query/name-builder/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/react-query/name-builder/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/react-query/name-builder/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/react-query/name-builder/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/react-query/name-builder/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/solid-query/asClass/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/solid-query/asClass/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/solid-query/asClass/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/solid-query/asClass/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/solid-query/asClass/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/solid-query/asClass/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/solid-query/asClass/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/solid-query/axios/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/solid-query/axios/client/index.ts
index 8ddc04f425..cff1d39c90 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/solid-query/axios/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/solid-query/axios/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/solid-query/axios/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/solid-query/axios/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/solid-query/axios/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/solid-query/fetch/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/solid-query/fetch/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/solid-query/fetch/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/solid-query/fetch/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/solid-query/fetch/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/solid-query/fetch/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/solid-query/fetch/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/solid-query/name-builder/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/solid-query/name-builder/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/solid-query/name-builder/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/solid-query/name-builder/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/solid-query/name-builder/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/solid-query/name-builder/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/solid-query/name-builder/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/svelte-query/asClass/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/svelte-query/asClass/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/svelte-query/asClass/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/svelte-query/asClass/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/svelte-query/asClass/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/svelte-query/asClass/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/svelte-query/asClass/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/svelte-query/axios/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/svelte-query/axios/client/index.ts
index 8ddc04f425..cff1d39c90 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/svelte-query/axios/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/svelte-query/axios/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/svelte-query/axios/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/svelte-query/axios/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/svelte-query/axios/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/svelte-query/fetch/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/svelte-query/fetch/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/svelte-query/fetch/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/svelte-query/fetch/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/svelte-query/fetch/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/svelte-query/fetch/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/svelte-query/fetch/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/svelte-query/name-builder/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/svelte-query/name-builder/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/svelte-query/name-builder/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/svelte-query/name-builder/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/svelte-query/name-builder/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/svelte-query/name-builder/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/svelte-query/name-builder/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/vue-query/asClass/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/vue-query/asClass/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/vue-query/asClass/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/vue-query/asClass/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/vue-query/asClass/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/vue-query/asClass/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/vue-query/asClass/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/vue-query/axios/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/vue-query/axios/client/index.ts
index 8ddc04f425..cff1d39c90 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/vue-query/axios/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/vue-query/axios/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/vue-query/axios/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/vue-query/axios/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/vue-query/axios/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/vue-query/fetch/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/vue-query/fetch/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/vue-query/fetch/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/vue-query/fetch/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/vue-query/fetch/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/vue-query/fetch/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/vue-query/fetch/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/vue-query/name-builder/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/vue-query/name-builder/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/vue-query/name-builder/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/vue-query/name-builder/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/vue-query/name-builder/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/vue-query/name-builder/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/plugins/@tanstack/vue-query/name-builder/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/security-api-key/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/security-api-key/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/security-api-key/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/security-api-key/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/security-api-key/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/security-api-key/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/security-api-key/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/security-false/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/security-false/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/security-false/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/security-false/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/security-false/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/security-false/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/security-false/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/security-http-bearer/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/security-http-bearer/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/security-http-bearer/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/security-http-bearer/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/security-http-bearer/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/security-http-bearer/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/security-http-bearer/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/security-oauth2/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/security-oauth2/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/security-oauth2/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/security-oauth2/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/security-oauth2/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/security-oauth2/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/security-oauth2/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/security-open-id-connect/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/security-open-id-connect/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/security-open-id-connect/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/security-open-id-connect/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/security-open-id-connect/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/security-open-id-connect/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/security-open-id-connect/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/servers/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/servers/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/servers/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/servers/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/servers/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/servers/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/servers/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-angular/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-angular/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-angular/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-angular/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-angular/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-angular/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-angular/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-axios/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-axios/client/index.ts
index 8ddc04f425..cff1d39c90 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-axios/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-axios/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-axios/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-axios/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-axios/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-fetch/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-fetch/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-fetch/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-fetch/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-fetch/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-fetch/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-fetch/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-next/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-next/client/index.ts
index 8ddc04f425..cff1d39c90 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-next/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-next/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-next/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-next/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-next/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-nuxt/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-nuxt/client/index.ts
index a2e8f2493f..f442748d17 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-nuxt/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-nuxt/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-nuxt/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-nuxt/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-nuxt/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-ofetch/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-ofetch/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-ofetch/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-ofetch/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-ofetch/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-ofetch/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/sse-ofetch/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-all-of/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-all-of/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-all-of/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-all-of/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-all-of/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-all-of/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-all-of/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-any-of-null/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-any-of-null/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-any-of-null/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-any-of-null/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-any-of-null/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-any-of-null/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-any-of-null/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transforms-read-write/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transforms-read-write/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transforms-read-write/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transforms-read-write/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transforms-read-write/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transforms-read-write/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transforms-read-write/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/plugins/@tanstack/meta/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/plugins/@tanstack/meta/client/index.ts
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/plugins/@tanstack/meta/client/index.ts
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/plugins/@tanstack/meta/client/index.ts
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/plugins/@tanstack/meta/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/plugins/@tanstack/meta/core/queryKeySerializer.gen.ts
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/plugins/@tanstack/meta/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/test/generated/v3_no_index/client/index.ts.snap b/packages/openapi-ts-tests/main/test/__snapshots__/test/generated/v3_no_index/client/index.ts.snap
index 318a84b6a8..cbf8dfeedb 100644
--- a/packages/openapi-ts-tests/main/test/__snapshots__/test/generated/v3_no_index/client/index.ts.snap
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/test/generated/v3_no_index/client/index.ts.snap
@@ -8,6 +8,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../core/bodySerializer.gen';
 export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
 export { createClient } from './client.gen';
 export type {
   Client,
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/test/generated/v3_no_index/core/queryKeySerializer.gen.ts.snap b/packages/openapi-ts-tests/main/test/__snapshots__/test/generated/v3_no_index/core/queryKeySerializer.gen.ts.snap
new file mode 100644
index 0000000000..d3bb68396e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/test/generated/v3_no_index/core/queryKeySerializer.gen.ts.snap
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/tsconfig/tsconfig.nodenext.json b/packages/openapi-ts-tests/main/test/tsconfig/tsconfig.nodenext.json
index 894f38263d..090bb97ca5 100644
--- a/packages/openapi-ts-tests/main/test/tsconfig/tsconfig.nodenext.json
+++ b/packages/openapi-ts-tests/main/test/tsconfig/tsconfig.nodenext.json
@@ -1,5 +1,5 @@
 {
-  "extends": "../../tsconfig.base.json",
+  "extends": "../../../tsconfig.base.json",
   "compilerOptions": {
     "declaration": false,
     "moduleResolution": "nodenext",
diff --git a/packages/openapi-ts/src/plugins/@hey-api/client-angular/bundle/index.ts b/packages/openapi-ts/src/plugins/@hey-api/client-angular/bundle/index.ts
index a237c773b0..c24fdc3b18 100644
--- a/packages/openapi-ts/src/plugins/@hey-api/client-angular/bundle/index.ts
+++ b/packages/openapi-ts/src/plugins/@hey-api/client-angular/bundle/index.ts
@@ -6,6 +6,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../../client-core/bundle/bodySerializer';
 export { buildClientParams } from '../../client-core/bundle/params';
+export { serializeQueryKeyValue } from '../../client-core/bundle/queryKeySerializer';
 export { createClient } from './client';
 export type {
   Client,
diff --git a/packages/openapi-ts/src/plugins/@hey-api/client-axios/bundle/index.ts b/packages/openapi-ts/src/plugins/@hey-api/client-axios/bundle/index.ts
index 1d5cdeebc4..39350a4f1a 100644
--- a/packages/openapi-ts/src/plugins/@hey-api/client-axios/bundle/index.ts
+++ b/packages/openapi-ts/src/plugins/@hey-api/client-axios/bundle/index.ts
@@ -6,6 +6,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../../client-core/bundle/bodySerializer';
 export { buildClientParams } from '../../client-core/bundle/params';
+export { serializeQueryKeyValue } from '../../client-core/bundle/queryKeySerializer';
 export { createClient } from './client';
 export type {
   Client,
diff --git a/packages/openapi-ts/src/plugins/@hey-api/client-core/__tests__/queryKeySerializer.test.ts b/packages/openapi-ts/src/plugins/@hey-api/client-core/__tests__/queryKeySerializer.test.ts
new file mode 100644
index 0000000000..d3e8c5f6aa
--- /dev/null
+++ b/packages/openapi-ts/src/plugins/@hey-api/client-core/__tests__/queryKeySerializer.test.ts
@@ -0,0 +1,111 @@
+import { describe, expect, it } from 'vitest';
+
+import {
+  queryKeyJsonReplacer,
+  serializeQueryKeyValue,
+  stringifyToJsonValue,
+} from '../bundle/queryKeySerializer';
+
+describe('query key helpers', () => {
+  describe('queryKeyJsonReplacer', () => {
+    it('converts bigint to string', () => {
+      expect(queryKeyJsonReplacer('value', 1n)).toBe('1');
+    });
+
+    it('converts Date to ISO string', () => {
+      const date = new Date('2025-01-01T12:34:56.000Z');
+      expect(queryKeyJsonReplacer('value', date)).toBe(date.toISOString());
+    });
+
+    it('drops unsupported values', () => {
+      expect(queryKeyJsonReplacer('value', undefined)).toBeUndefined();
+      expect(queryKeyJsonReplacer('value', () => {})).toBeUndefined();
+      expect(queryKeyJsonReplacer('value', Symbol('s'))).toBeUndefined();
+    });
+  });
+
+  describe('stringifyToJsonValue', () => {
+    it('produces JSON-safe structures', () => {
+      const input = {
+        a: 1n,
+        b: new Date('2025-01-02T00:00:00.000Z'),
+        c: () => {},
+        d: undefined,
+      };
+
+      expect(stringifyToJsonValue(input)).toEqual({
+        a: '1',
+        b: '2025-01-02T00:00:00.000Z',
+      });
+    });
+
+    it('returns undefined when value cannot be stringified', () => {
+      const circular: { self?: unknown } = {};
+      circular.self = circular;
+
+      expect(stringifyToJsonValue(circular)).toBeUndefined();
+    });
+  });
+
+  describe('serializeQueryKeyValue', () => {
+    it('handles primitives and null', () => {
+      expect(serializeQueryKeyValue(null)).toBeNull();
+      expect(serializeQueryKeyValue('')).toBe('');
+      expect(serializeQueryKeyValue(0)).toBe(0);
+      expect(serializeQueryKeyValue(false)).toBe(false);
+    });
+
+    it('converts special primitives', () => {
+      expect(serializeQueryKeyValue(1n)).toBe('1');
+
+      const date = new Date('2025-03-04T05:06:07.000Z');
+      expect(serializeQueryKeyValue(date)).toBe(date.toISOString());
+    });
+
+    it('normalizes arrays', () => {
+      const date = new Date('2025-03-04T05:06:07.000Z');
+      expect(
+        serializeQueryKeyValue([1n, date, undefined, () => {}, 'ok']),
+      ).toEqual(['1', date.toISOString(), null, null, 'ok']);
+    });
+
+    it('normalizes plain objects', () => {
+      const result = serializeQueryKeyValue({
+        a: 1,
+        b: 1n,
+        c: new Date('2025-06-07T08:09:10.000Z'),
+        d: undefined,
+        e: () => {},
+      });
+
+      expect(result).toEqual({
+        a: 1,
+        b: '1',
+        c: '2025-06-07T08:09:10.000Z',
+      });
+    });
+
+    it('supports objects with null prototype', () => {
+      const value = Object.assign(Object.create(null), { a: 1 });
+      expect(serializeQueryKeyValue(value)).toEqual({ a: 1 });
+    });
+
+    it('serializes URLSearchParams as JSON object', () => {
+      const params = new URLSearchParams();
+      params.append('a', '1');
+      params.append('a', '2');
+      params.append('b', 'foo');
+
+      expect(serializeQueryKeyValue(params)).toEqual({
+        a: ['1', '2'],
+        b: 'foo',
+      });
+    });
+
+    it('rejects unsupported structures', () => {
+      expect(serializeQueryKeyValue(new Map())).toBeUndefined();
+      expect(serializeQueryKeyValue(new Set())).toBeUndefined();
+      expect(serializeQueryKeyValue(new (class Example {})())).toBeUndefined();
+    });
+  });
+});
diff --git a/packages/openapi-ts/src/plugins/@hey-api/client-core/bundle/queryKeySerializer.ts b/packages/openapi-ts/src/plugins/@hey-api/client-core/bundle/queryKeySerializer.ts
new file mode 100644
index 0000000000..b708f22c96
--- /dev/null
+++ b/packages/openapi-ts/src/plugins/@hey-api/client-core/bundle/queryKeySerializer.ts
@@ -0,0 +1,134 @@
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts/src/plugins/@hey-api/client-fetch/bundle/index.ts b/packages/openapi-ts/src/plugins/@hey-api/client-fetch/bundle/index.ts
index a237c773b0..c24fdc3b18 100644
--- a/packages/openapi-ts/src/plugins/@hey-api/client-fetch/bundle/index.ts
+++ b/packages/openapi-ts/src/plugins/@hey-api/client-fetch/bundle/index.ts
@@ -6,6 +6,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../../client-core/bundle/bodySerializer';
 export { buildClientParams } from '../../client-core/bundle/params';
+export { serializeQueryKeyValue } from '../../client-core/bundle/queryKeySerializer';
 export { createClient } from './client';
 export type {
   Client,
diff --git a/packages/openapi-ts/src/plugins/@hey-api/client-next/bundle/index.ts b/packages/openapi-ts/src/plugins/@hey-api/client-next/bundle/index.ts
index 1d5cdeebc4..39350a4f1a 100644
--- a/packages/openapi-ts/src/plugins/@hey-api/client-next/bundle/index.ts
+++ b/packages/openapi-ts/src/plugins/@hey-api/client-next/bundle/index.ts
@@ -6,6 +6,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../../client-core/bundle/bodySerializer';
 export { buildClientParams } from '../../client-core/bundle/params';
+export { serializeQueryKeyValue } from '../../client-core/bundle/queryKeySerializer';
 export { createClient } from './client';
 export type {
   Client,
diff --git a/packages/openapi-ts/src/plugins/@hey-api/client-nuxt/bundle/index.ts b/packages/openapi-ts/src/plugins/@hey-api/client-nuxt/bundle/index.ts
index 2c17fa8288..cc8c9d8166 100644
--- a/packages/openapi-ts/src/plugins/@hey-api/client-nuxt/bundle/index.ts
+++ b/packages/openapi-ts/src/plugins/@hey-api/client-nuxt/bundle/index.ts
@@ -6,6 +6,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../../client-core/bundle/bodySerializer';
 export { buildClientParams } from '../../client-core/bundle/params';
+export { serializeQueryKeyValue } from '../../client-core/bundle/queryKeySerializer';
 export { createClient } from './client';
 export type {
   Client,
diff --git a/packages/openapi-ts/src/plugins/@hey-api/client-ofetch/bundle/index.ts b/packages/openapi-ts/src/plugins/@hey-api/client-ofetch/bundle/index.ts
index a237c773b0..c24fdc3b18 100644
--- a/packages/openapi-ts/src/plugins/@hey-api/client-ofetch/bundle/index.ts
+++ b/packages/openapi-ts/src/plugins/@hey-api/client-ofetch/bundle/index.ts
@@ -6,6 +6,7 @@ export {
   urlSearchParamsBodySerializer,
 } from '../../client-core/bundle/bodySerializer';
 export { buildClientParams } from '../../client-core/bundle/params';
+export { serializeQueryKeyValue } from '../../client-core/bundle/queryKeySerializer';
 export { createClient } from './client';
 export type {
   Client,
diff --git a/packages/openapi-ts/src/plugins/@pinia/colada/api.ts b/packages/openapi-ts/src/plugins/@pinia/colada/api.ts
index 8b41d45a35..171c8310c7 100644
--- a/packages/openapi-ts/src/plugins/@pinia/colada/api.ts
+++ b/packages/openapi-ts/src/plugins/@pinia/colada/api.ts
@@ -6,8 +6,10 @@ type SelectorType =
   | '_JSONValue'
   | 'AxiosError'
   | 'createQueryKey'
-  | 'queryOptionsFn'
+  | 'defineQueryOptions'
   | 'QueryKey'
+  | 'queryOptionsFn'
+  | 'serializeQueryKeyValue'
   | 'UseMutationOptions'
   | 'UseQueryOptions';
 
@@ -18,8 +20,10 @@ export type IApi = {
    *  - `_JSONValue`: never
    *  - `AxiosError`: never
    *  - `createQueryKey`: never
-   *  - `queryOptionsFn`: `operation.id` string
+   *  - `defineQueryOptions`: never
    *  - `QueryKey`: never
+   *  - `queryOptionsFn`: `operation.id` string
+   *  - `serializeQueryKeyValue`: never
    *  - `UseMutationOptions`: never
    *  - `UseQueryOptions`: never
    * @returns Selector array
diff --git a/packages/openapi-ts/src/plugins/@pinia/colada/queryKey.ts b/packages/openapi-ts/src/plugins/@pinia/colada/queryKey.ts
index 6903791614..ea619179ed 100644
--- a/packages/openapi-ts/src/plugins/@pinia/colada/queryKey.ts
+++ b/packages/openapi-ts/src/plugins/@pinia/colada/queryKey.ts
@@ -1,6 +1,7 @@
 import type { Symbol } from '@hey-api/codegen-core';
 import type { Expression } from 'typescript';
 
+import { clientFolderAbsolutePath } from '../../../generate/client';
 import { hasOperationDataRequired } from '../../../ir/operation';
 import type { IR } from '../../../ir/types';
 import { buildName } from '../../../openApi/shared/utils/name';
@@ -34,6 +35,9 @@ export const createQueryKeyFunction = ({
   const symbolQueryKeyType = plugin.referenceSymbol(
     plugin.api.getSelector('QueryKey'),
   );
+  const symbolJsonValue = plugin.referenceSymbol(
+    plugin.api.getSelector('_JSONValue'),
+  );
 
   const returnType = tsc.indexedAccessTypeNode({
     indexType: tsc.literalTypeNode({
@@ -60,6 +64,12 @@ export const createQueryKeyFunction = ({
         )
       : undefined;
 
+  const clientModule = clientFolderAbsolutePath(plugin.context.config);
+  const symbolSerializeQueryValue = plugin.registerSymbol({
+    external: clientModule,
+    name: 'serializeQueryKeyValue',
+  });
+
   const fn = tsc.constVariable({
     expression: tsc.arrowFunction({
       multiLine: true,
@@ -88,10 +98,7 @@ export const createQueryKeyFunction = ({
           expression: tsc.objectExpression({
             multiLine: false,
             obj: [
-              {
-                key: '_id',
-                value: tsc.identifier({ text: 'id' }),
-              },
+              { key: '_id', value: tsc.identifier({ text: 'id' }) },
               {
                 key: baseUrlKey,
                 value: tsc.identifier({
@@ -118,7 +125,9 @@ export const createQueryKeyFunction = ({
                       expression: tsc.identifier({ text: 'tags' }),
                       type: tsc.keywordTypeNode({ keyword: 'unknown' }),
                     }),
-                    type: tsc.keywordTypeNode({ keyword: 'undefined' }),
+                    type: tsc.typeReferenceNode({
+                      typeName: symbolJsonValue.placeholder,
+                    }),
                   }),
                 }),
               }),
@@ -126,52 +135,47 @@ export const createQueryKeyFunction = ({
           }),
         }),
         tsc.ifStatement({
-          expression: tsc.propertyAccessExpression({
-            expression: optionsIdentifier,
-            isOptional: true,
-            name: tsc.identifier({ text: 'body' }),
+          expression: tsc.binaryExpression({
+            left: tsc.propertyAccessExpression({
+              expression: optionsIdentifier,
+              isOptional: true,
+              name: tsc.identifier({ text: 'body' }),
+            }),
+            operator: '!==',
+            right: 'undefined',
           }),
           thenStatement: tsc.block({
             statements: [
-              tsc.expressionToStatement({
-                expression: tsc.binaryExpression({
-                  left: tsc.propertyAccessExpression({
-                    expression: 'params',
-                    name: 'body',
-                  }),
-                  right: tsc.propertyAccessExpression({
-                    expression: 'options',
-                    name: 'body',
-                  }),
+              tsc.constVariable({
+                expression: tsc.callExpression({
+                  functionName: symbolSerializeQueryValue.placeholder,
+                  parameters: [
+                    tsc.propertyAccessExpression({
+                      expression: 'options',
+                      name: 'body',
+                    }),
+                  ],
                 }),
+                name: 'normalizedBody',
               }),
-            ],
-          }),
-        }),
-        tsc.ifStatement({
-          expression: tsc.propertyAccessExpression({
-            expression: optionsIdentifier,
-            isOptional: true,
-            name: tsc.identifier({ text: 'headers' }),
-          }),
-          thenStatement: tsc.block({
-            statements: [
-              tsc.expressionToStatement({
+              tsc.ifStatement({
                 expression: tsc.binaryExpression({
-                  left: tsc.propertyAccessExpression({
-                    expression: 'params',
-                    name: 'headers',
-                  }),
-                  right: tsc.asExpression({
-                    expression: tsc.asExpression({
-                      expression: tsc.propertyAccessExpression({
-                        expression: 'options',
-                        name: 'headers',
+                  left: tsc.identifier({ text: 'normalizedBody' }),
+                  operator: '!==',
+                  right: 'undefined',
+                }),
+                thenStatement: tsc.block({
+                  statements: [
+                    tsc.expressionToStatement({
+                      expression: tsc.binaryExpression({
+                        left: tsc.propertyAccessExpression({
+                          expression: 'params',
+                          name: 'body',
+                        }),
+                        right: tsc.identifier({ text: 'normalizedBody' }),
                       }),
-                      type: tsc.keywordTypeNode({ keyword: 'unknown' }),
                     }),
-                    type: tsc.keywordTypeNode({ keyword: 'undefined' }),
-                  }),
+                  ],
                 }),
               }),
             ],
@@ -201,29 +205,47 @@ export const createQueryKeyFunction = ({
           }),
         }),
         tsc.ifStatement({
-          expression: tsc.propertyAccessExpression({
-            expression: optionsIdentifier,
-            isOptional: true,
-            name: tsc.identifier({ text: 'query' }),
+          expression: tsc.binaryExpression({
+            left: tsc.propertyAccessExpression({
+              expression: optionsIdentifier,
+              isOptional: true,
+              name: tsc.identifier({ text: 'query' }),
+            }),
+            operator: '!==',
+            right: 'undefined',
           }),
           thenStatement: tsc.block({
             statements: [
-              tsc.expressionToStatement({
+              tsc.constVariable({
+                expression: tsc.callExpression({
+                  functionName: symbolSerializeQueryValue.placeholder,
+                  parameters: [
+                    tsc.propertyAccessExpression({
+                      expression: 'options',
+                      name: 'query',
+                    }),
+                  ],
+                }),
+                name: 'normalizedQuery',
+              }),
+              tsc.ifStatement({
                 expression: tsc.binaryExpression({
-                  left: tsc.propertyAccessExpression({
-                    expression: 'params',
-                    name: 'query',
-                  }),
-                  right: tsc.asExpression({
-                    expression: tsc.asExpression({
-                      expression: tsc.propertyAccessExpression({
-                        expression: 'options',
-                        name: 'query',
+                  left: tsc.identifier({ text: 'normalizedQuery' }),
+                  operator: '!==',
+                  right: 'undefined',
+                }),
+                thenStatement: tsc.block({
+                  statements: [
+                    tsc.expressionToStatement({
+                      expression: tsc.binaryExpression({
+                        left: tsc.propertyAccessExpression({
+                          expression: 'params',
+                          name: 'query',
+                        }),
+                        right: tsc.identifier({ text: 'normalizedQuery' }),
                       }),
-                      type: tsc.keywordTypeNode({ keyword: 'unknown' }),
                     }),
-                    type: tsc.keywordTypeNode({ keyword: 'undefined' }),
-                  }),
+                  ],
                 }),
               }),
             ],
@@ -286,10 +308,7 @@ export const createQueryKeyType = ({
   );
 
   const properties: Array<Property> = [
-    {
-      name: '_id',
-      type: tsc.keywordTypeNode({ keyword: 'string' }),
-    },
+    { name: '_id', type: tsc.keywordTypeNode({ keyword: 'string' }) },
     {
       isRequired: false,
       name: getClientBaseUrlKey(plugin.context.config),
@@ -297,7 +316,7 @@ export const createQueryKeyType = ({
     },
     {
       isRequired: false,
-      name: 'headers',
+      name: 'body',
       type: tsc.typeReferenceNode({ typeName: symbolJsonValue.placeholder }),
     },
     {
@@ -318,9 +337,7 @@ export const createQueryKeyType = ({
   );
   const symbolQueryKeyType = plugin.registerSymbol({
     exported: true,
-    meta: {
-      kind: 'type',
-    },
+    meta: { kind: 'type' },
     name: 'QueryKey',
     selector: plugin.api.getSelector('QueryKey'),
   });
@@ -332,7 +349,7 @@ export const createQueryKeyType = ({
         tsc.typeIntersectionNode({
           types: [
             tsc.typeReferenceNode({
-              typeName: `Pick<${TOptionsType}, 'body' | 'path'>`,
+              typeName: `Pick<${TOptionsType}, 'path'>`,
             }),
             tsc.typeInterfaceNode({
               properties,
diff --git a/packages/openapi-ts/src/plugins/@pinia/colada/queryOptions.ts b/packages/openapi-ts/src/plugins/@pinia/colada/queryOptions.ts
index 6449279b57..2e0ef5a0cd 100644
--- a/packages/openapi-ts/src/plugins/@pinia/colada/queryOptions.ts
+++ b/packages/openapi-ts/src/plugins/@pinia/colada/queryOptions.ts
@@ -15,11 +15,11 @@ import {
   queryKeyStatement,
 } from './queryKey';
 import type { PiniaColadaPlugin } from './types';
-import { useTypeData, useTypeError, useTypeResponse } from './useType';
+import { useTypeData } from './useType';
 import { getPublicTypeData } from './utils';
 
-const fnOptions = 'context';
 const optionsParamName = 'options';
+const fnOptions = 'context';
 
 export const createQueryOptions = ({
   operation,
@@ -38,38 +38,56 @@ export const createQueryOptions = ({
     context: plugin.context,
     operation,
   });
-
   if (!plugin.getSymbol(plugin.api.getSelector('createQueryKey'))) {
     createQueryKeyType({ plugin });
     createQueryKeyFunction({ plugin });
   }
 
-  const symbolUseQueryOptions = plugin.referenceSymbol(
-    plugin.api.getSelector('UseQueryOptions'),
-  );
-
-  const symbolQueryKey = plugin.registerSymbol({
-    exported: true,
-    name: buildName({
-      config: plugin.config.queryKeys,
-      name: operation.id,
-    }),
-  });
-  const node = queryKeyStatement({
-    operation,
-    plugin,
-    symbol: symbolQueryKey,
-  });
-  plugin.setSymbolValue(symbolQueryKey, node);
+  let keyExpression: ts.Expression;
+  if (plugin.config.queryKeys.enabled) {
+    const symbolQueryKey = plugin.registerSymbol({
+      exported: true,
+      name: buildName({
+        config: plugin.config.queryKeys,
+        name: operation.id,
+      }),
+    });
+    const node = queryKeyStatement({
+      operation,
+      plugin,
+      symbol: symbolQueryKey,
+    });
+    plugin.setSymbolValue(symbolQueryKey, node);
+    keyExpression = tsc.callExpression({
+      functionName: symbolQueryKey.placeholder,
+      parameters: [optionsParamName],
+    });
+  } else {
+    const symbolCreateQueryKey = plugin.referenceSymbol(
+      plugin.api.getSelector('createQueryKey'),
+    );
+    // Optionally include tags when configured
+    let tagsExpr: ts.Expression | undefined;
+    if (
+      plugin.config.queryKeys.tags &&
+      operation.tags &&
+      operation.tags.length > 0
+    ) {
+      tagsExpr = tsc.arrayLiteralExpression({
+        elements: operation.tags.map((t) => tsc.stringLiteral({ text: t })),
+      });
+    }
+    keyExpression = tsc.callExpression({
+      functionName: symbolCreateQueryKey.placeholder,
+      parameters: [tsc.ots.string(operation.id), optionsParamName, tagsExpr],
+    });
+  }
 
   const typeData = useTypeData({ operation, plugin });
-  const typeError = useTypeError({ operation, plugin });
-  const typeResponse = useTypeResponse({ operation, plugin });
-  const { isNuxtClient, strippedTypeData } = getPublicTypeData({
+  const { strippedTypeData } = getPublicTypeData({
     plugin,
     typeData,
   });
-
   const awaitSdkExpression = tsc.awaitExpression({
     expression: tsc.callExpression({
       functionName: queryFn,
@@ -77,16 +95,9 @@ export const createQueryOptions = ({
         tsc.objectExpression({
           multiLine: true,
           obj: [
-            {
-              spread: optionsParamName,
-            },
-            {
-              spread: fnOptions,
-            },
-            {
-              key: 'throwOnError',
-              value: true,
-            },
+            { spread: optionsParamName },
+            { spread: fnOptions },
+            { key: 'throwOnError', value: true },
           ],
         }),
       ],
@@ -94,7 +105,6 @@ export const createQueryOptions = ({
   });
 
   const statements: Array<ts.Statement> = [];
-
   if (plugin.getPluginOrThrow('@hey-api/sdk').config.responseStyle === 'data') {
     statements.push(
       tsc.returnVariable({
@@ -117,31 +127,20 @@ export const createQueryOptions = ({
   const queryOptionsObj: Array<{ key: string; value: ts.Expression }> = [
     {
       key: 'key',
-      value: tsc.callExpression({
-        functionName: symbolQueryKey.placeholder,
-        parameters: [optionsParamName],
-      }),
+      value: keyExpression,
     },
     {
       key: 'query',
       value: tsc.arrowFunction({
         async: true,
         multiLine: true,
-        parameters: [
-          isNuxtClient
-            ? {
-                name: fnOptions,
-                type: strippedTypeData,
-              }
-            : { name: fnOptions },
-        ],
+        parameters: [{ name: fnOptions }],
         statements,
       }),
     },
   ];
 
   const meta = handleMeta(plugin, operation, 'queryOptions');
-
   if (meta) {
     queryOptionsObj.push({
       key: 'meta',
@@ -157,28 +156,28 @@ export const createQueryOptions = ({
     }),
     selector: plugin.api.getSelector('queryOptionsFn', operation.id),
   });
+  const symbolDefineQueryOptions = plugin.registerSymbol({
+    external: plugin.name,
+    name: 'defineQueryOptions',
+    selector: plugin.api.getSelector('defineQueryOptions'),
+  });
   const statement = tsc.constVariable({
     comment: plugin.config.comments
       ? createOperationComment({ operation })
       : undefined,
     exportConst: symbolQueryOptionsFn.exported,
-    expression: tsc.arrowFunction({
+    expression: tsc.callExpression({
+      functionName: symbolDefineQueryOptions.placeholder,
       parameters: [
-        {
-          isRequired: isRequiredOptions,
-          name: optionsParamName,
-          type: strippedTypeData,
-        },
-      ],
-      // TODO: better types syntax
-      returnType: isNuxtClient
-        ? `${symbolUseQueryOptions.placeholder}<${typeResponse}, ${strippedTypeData}, ${typeError}>`
-        : `${symbolUseQueryOptions.placeholder}<${typeResponse}, ${typeError}>`,
-      statements: [
-        tsc.returnStatement({
-          expression: tsc.objectExpression({
-            obj: queryOptionsObj,
-          }),
+        tsc.arrowFunction({
+          parameters: [
+            {
+              isRequired: isRequiredOptions,
+              name: optionsParamName,
+              type: strippedTypeData,
+            },
+          ],
+          statements: tsc.objectExpression({ obj: queryOptionsObj }),
         }),
       ],
     }),
diff --git a/packages/openapi-ts/src/tsc/transform.ts b/packages/openapi-ts/src/tsc/transform.ts
index 1ae12e14bd..f6f3253e83 100644
--- a/packages/openapi-ts/src/tsc/transform.ts
+++ b/packages/openapi-ts/src/tsc/transform.ts
@@ -67,7 +67,7 @@ export const createBinaryExpression = ({
   right,
 }: {
   left: ts.Expression;
-  operator?: '=' | '===' | 'in' | '??';
+  operator?: '=' | '===' | '!==' | 'in' | '??';
   right: ts.Expression | string;
 }) => {
   const expression = ts.factory.createBinaryExpression(
@@ -77,9 +77,11 @@ export const createBinaryExpression = ({
       ? ts.SyntaxKind.EqualsToken
       : operator === '==='
         ? ts.SyntaxKind.EqualsEqualsEqualsToken
-        : operator === '??'
-          ? ts.SyntaxKind.QuestionQuestionToken
-          : ts.SyntaxKind.InKeyword,
+        : operator === '!=='
+          ? ts.SyntaxKind.ExclamationEqualsEqualsToken
+          : operator === '??'
+            ? ts.SyntaxKind.QuestionQuestionToken
+            : ts.SyntaxKind.InKeyword,
     typeof right === 'string' ? createIdentifier({ text: right }) : right,
   );
   return expression;