diff --git a/CHANGELOG.md b/CHANGELOG.md
index 605aabbf3..2446e5f49 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1 +1,2 @@
 - Add an authPolicy callback to CallableOptions for reusable auth middleware as well as helper auth policies (#1650)
+- Multiple breaking changes to the not-yet-announced streaming feature for Callable Functions (#1652)
diff --git a/spec/common/providers/https.spec.ts b/spec/common/providers/https.spec.ts
index ef77a6fa6..86e1b8696 100644
--- a/spec/common/providers/https.spec.ts
+++ b/spec/common/providers/https.spec.ts
@@ -770,7 +770,7 @@ describe("onCallHandler", () => {
           cors: { origin: true, methods: "POST" },
         },
         (req, resp) => {
-          resp.write("hello");
+          resp.sendChunk("hello");
           return "world";
         },
         "gcfv2"
@@ -840,10 +840,10 @@ describe("onCallHandler", () => {
         {
           cors: { origin: true, methods: "POST" },
         },
-        (req, resp) => {
-          resp.write("initial message");
-          mockReq.emit("close");
-          resp.write("should not be sent");
+        async (req, resp) => {
+          await resp.sendChunk("initial message");
+          await mockReq.emit("close");
+          await resp.sendChunk("should not be sent");
           return "done";
         },
         "gcfv2"
@@ -908,7 +908,7 @@ describe("onCallHandler", () => {
           },
           async (resp, res) => {
             await new Promise((resolve) => setTimeout(resolve, 3_000));
-            res.write("hello");
+            res.sendChunk("hello");
             await new Promise((resolve) => setTimeout(resolve, 3_000));
             return "done";
           },
diff --git a/spec/helper.ts b/spec/helper.ts
index 5c8ca0c76..04829be38 100644
--- a/spec/helper.ts
+++ b/spec/helper.ts
@@ -84,8 +84,11 @@ export function runHandler(
         }
       }
 
-      public write(writeBody: any) {
+      public write(writeBody: any, cb?: () => void) {
         this.sentBody += typeof writeBody === "object" ? JSON.stringify(writeBody) : writeBody;
+        if (cb) {
+          setImmediate(cb);
+        }
         return true;
       }
 
diff --git a/src/common/providers/https.ts b/src/common/providers/https.ts
index 24300cf9d..a6989f130 100644
--- a/src/common/providers/https.ts
+++ b/src/common/providers/https.ts
@@ -141,23 +141,30 @@ export interface CallableRequest<T = any> {
    * The raw request handled by the callable.
    */
   rawRequest: Request;
+
+  /**
+   * Whether this is a streaming request.
+   * Code can be optimized by not trying to generate a stream of chunks to
+   * call response.sendChunk on if request.acceptsStreaming is false.
+   * It is always safe, however, to call response.sendChunk as this will
+   * noop if acceptsStreaming is false.
+   */
+  acceptsStreaming: boolean;
 }
 
 /**
- * CallableProxyResponse exposes subset of express.Response object
- * to allow writing partial, streaming responses back to the client.
+ * CallableProxyResponse allows streaming response chunks and listening to signals
+ * triggered in events such as a disconnect.
  */
-export interface CallableProxyResponse {
+export interface CallableResponse<T = unknown> {
   /**
    * Writes a chunk of the response body to the client. This method can be called
    * multiple times to stream data progressively.
+   * Returns a promise of whether the data was written. This can be false, for example,
+   * if the request was not a streaming request. Rejects if there is a network error.
    */
-  write: express.Response["write"];
-  /**
-   * Indicates whether the client has requested and can handle streaming responses.
-   * This should be checked before attempting to stream data to avoid compatibility issues.
-   */
-  acceptsStreaming: boolean;
+  sendChunk: (chunk: T) => Promise<boolean>;
+
   /**
    * An AbortSignal that is triggered when the client disconnects or the
    * request is terminated prematurely.
@@ -586,13 +593,9 @@ async function checkTokens(
     auth: "INVALID",
   };
 
-  await Promise.all([
-    Promise.resolve().then(async () => {
-      verifications.auth = await checkAuthToken(req, ctx);
-    }),
-    Promise.resolve().then(async () => {
-      verifications.app = await checkAppCheckToken(req, ctx, options);
-    }),
+  [verifications.auth, verifications.app] = await Promise.all([
+    checkAuthToken(req, ctx),
+    checkAppCheckToken(req, ctx, options),
   ]);
 
   const logPayload = {
@@ -697,9 +700,9 @@ async function checkAppCheckToken(
 }
 
 type v1CallableHandler = (data: any, context: CallableContext) => any | Promise<any>;
-type v2CallableHandler<Req, Res> = (
+type v2CallableHandler<Req, Res, Stream> = (
   request: CallableRequest<Req>,
-  response?: CallableProxyResponse
+  response?: CallableResponse<Stream>
 ) => Res;
 
 /** @internal **/
@@ -718,9 +721,9 @@ export interface CallableOptions<T = any> {
 }
 
 /** @internal */
-export function onCallHandler<Req = any, Res = any>(
+export function onCallHandler<Req = any, Res = any, Stream = unknown>(
   options: CallableOptions<Req>,
-  handler: v1CallableHandler | v2CallableHandler<Req, Res>,
+  handler: v1CallableHandler | v2CallableHandler<Req, Res, Stream>,
   version: "gcfv1" | "gcfv2"
 ): (req: Request, res: express.Response) => Promise<void> {
   const wrapped = wrapOnCallHandler(options, handler, version);
@@ -739,9 +742,9 @@ function encodeSSE(data: unknown): string {
 }
 
 /** @internal */
-function wrapOnCallHandler<Req = any, Res = any>(
+function wrapOnCallHandler<Req = any, Res = any, Stream = unknown>(
   options: CallableOptions<Req>,
-  handler: v1CallableHandler | v2CallableHandler<Req, Res>,
+  handler: v1CallableHandler | v2CallableHandler<Req, Res, Stream>,
   version: "gcfv1" | "gcfv2"
 ): (req: Request, res: express.Response) => Promise<void> {
   return async (req: Request, res: express.Response): Promise<void> => {
@@ -855,27 +858,41 @@ function wrapOnCallHandler<Req = any, Res = any>(
         const arg: CallableRequest<Req> = {
           ...context,
           data,
+          acceptsStreaming,
         };
 
-        const responseProxy: CallableProxyResponse = {
-          write(chunk): boolean {
+        const responseProxy: CallableResponse<Stream> = {
+          sendChunk(chunk: Stream): Promise<boolean> {
             // if client doesn't accept sse-protocol, response.write() is no-op.
             if (!acceptsStreaming) {
-              return false;
+              return Promise.resolve(false);
             }
             // if connection is already closed, response.write() is no-op.
             if (abortController.signal.aborted) {
-              return false;
+              return Promise.resolve(false);
             }
             const formattedData = encodeSSE({ message: chunk });
-            const wrote = res.write(formattedData);
+            let resolve: (wrote: boolean) => void;
+            let reject: (err: Error) => void;
+            const p = new Promise<boolean>((res, rej) => {
+              resolve = res;
+              reject = rej;
+            });
+            const wrote = res.write(formattedData, (error) => {
+              if (error) {
+                reject(error);
+                return;
+              }
+              resolve(wrote);
+            });
+
             // Reset heartbeat timer after successful write
             if (wrote && heartbeatInterval !== null && heartbeatSeconds > 0) {
               scheduleHeartbeat();
             }
-            return wrote;
+
+            return p;
           },
-          acceptsStreaming,
           signal: abortController.signal,
         };
         if (acceptsStreaming) {
diff --git a/src/v2/providers/https.ts b/src/v2/providers/https.ts
index 0a5b3e8c3..e59ce9704 100644
--- a/src/v2/providers/https.ts
+++ b/src/v2/providers/https.ts
@@ -33,7 +33,7 @@ import { isDebugFeatureEnabled } from "../../common/debug";
 import { ResetValue } from "../../common/options";
 import {
   CallableRequest,
-  CallableProxyResponse,
+  CallableResponse,
   FunctionsErrorCode,
   HttpsError,
   onCallHandler,
@@ -258,12 +258,17 @@ export type HttpsFunction = ((
 /**
  * Creates a callable method for clients to call using a Firebase SDK.
  */
-export interface CallableFunction<T, Return> extends HttpsFunction {
+export interface CallableFunction<T, Return, Stream = unknown> extends HttpsFunction {
   /** Executes the handler function with the provided data as input. Used for unit testing.
    * @param data - An input for the handler function.
    * @returns The output of the handler function.
    */
-  run(data: CallableRequest<T>): Return;
+  run(request: CallableRequest<T>): Return;
+
+  stream(
+    request: CallableRequest<T>,
+    response: CallableResponse<Stream>
+  ): { stream: AsyncIterator<Stream>; output: Return };
 }
 
 /**
@@ -387,22 +392,22 @@ export function onRequest(
  * @param handler - A function that takes a {@link https.CallableRequest}.
  * @returns A function that you can export and deploy.
  */
-export function onCall<T = any, Return = any | Promise<any>>(
+export function onCall<T = any, Return = any | Promise<any>, Stream = unknown>(
   opts: CallableOptions<T>,
-  handler: (request: CallableRequest<T>, response?: CallableProxyResponse) => Return
-): CallableFunction<T, Return extends Promise<unknown> ? Return : Promise<Return>>;
+  handler: (request: CallableRequest<T>, response?: CallableResponse<Stream>) => Return
+): CallableFunction<T, Return extends Promise<unknown> ? Return : Promise<Return>, Stream>;
 
 /**
  * Declares a callable method for clients to call using a Firebase SDK.
  * @param handler - A function that takes a {@link https.CallableRequest}.
  * @returns A function that you can export and deploy.
  */
-export function onCall<T = any, Return = any | Promise<any>>(
-  handler: (request: CallableRequest<T>, response?: CallableProxyResponse) => Return
+export function onCall<T = any, Return = any | Promise<any>, Stream = unknown>(
+  handler: (request: CallableRequest<T>, response?: CallableResponse<Stream>) => Return
 ): CallableFunction<T, Return extends Promise<unknown> ? Return : Promise<Return>>;
-export function onCall<T = any, Return = any | Promise<any>>(
+export function onCall<T = any, Return = any | Promise<any>, Stream = unknown>(
   optsOrHandler: CallableOptions<T> | ((request: CallableRequest<T>) => Return),
-  handler?: (request: CallableRequest<T>, response?: CallableProxyResponse) => Return
+  handler?: (request: CallableRequest<T>, response?: CallableResponse<Stream>) => Return
 ): CallableFunction<T, Return extends Promise<unknown> ? Return : Promise<Return>> {
   let opts: CallableOptions;
   if (arguments.length === 1) {
@@ -421,7 +426,7 @@ export function onCall<T = any, Return = any | Promise<any>>(
   }
 
   // fix the length of handler to make the call to handler consistent
-  const fixedLen = (req: CallableRequest<T>, resp?: CallableProxyResponse) => handler(req, resp);
+  const fixedLen = (req: CallableRequest<T>, resp?: CallableResponse<Stream>) => handler(req, resp);
   let func: any = onCallHandler(
     {
       cors: { origin, methods: "POST" },
@@ -474,6 +479,17 @@ export function onCall<T = any, Return = any | Promise<any>>(
     callableTrigger: {},
   };
 
+  // TODO: in the next major version, do auth/appcheck in these helper methods too.
   func.run = withInit(handler);
+  func.stream = () => {
+    return {
+      stream: {
+        next(): Promise<IteratorResult<Stream>> {
+          return Promise.reject("Coming soon");
+        },
+      },
+      output: Promise.reject("Coming soon"),
+    };
+  };
   return func;
 }