diff --git a/generators/typescript/sdk/client-class-generator/src/websocket/GeneratedDefaultWebsocketImplementation.ts b/generators/typescript/sdk/client-class-generator/src/websocket/GeneratedDefaultWebsocketImplementation.ts
index 6bd5dec101ba..cd4ce880251b 100644
--- a/generators/typescript/sdk/client-class-generator/src/websocket/GeneratedDefaultWebsocketImplementation.ts
+++ b/generators/typescript/sdk/client-class-generator/src/websocket/GeneratedDefaultWebsocketImplementation.ts
@@ -173,16 +173,18 @@ export class GeneratedDefaultWebsocketImplementation implements GeneratedWebsock
                 }),
                 ...(this.channel.queryParameters ?? []).map((queryParameter) => {
                     const type = context.type.getReferenceToType(queryParameter.valueType);
+                    const isOptional = context.type.isOptional(queryParameter.valueType);
                     const typeNode = queryParameter.allowMultiple
                         ? ts.factory.createUnionTypeNode([
                               type.typeNodeWithoutUndefined,
-                              ts.factory.createArrayTypeNode(type.typeNodeWithoutUndefined)
+                              ts.factory.createArrayTypeNode(type.typeNodeWithoutUndefined),
+                              ...(isOptional ? [ts.factory.createKeywordTypeNode(ts.SyntaxKind.UndefinedKeyword)] : [])
                           ])
                         : type.typeNodeWithoutUndefined;
                     return {
                         name: getPropertyKey(this.getPropertyNameOfQueryParameter(queryParameter).propertyName),
                         type: getTextOfTsNode(typeNode),
-                        hasQuestionToken: context.type.isOptional(queryParameter.valueType)
+                        hasQuestionToken: isOptional
                     };
                 }),
                 ...(this.channel.headers ?? []).map((header) => {
diff --git a/generators/typescript/sdk/versions.yml b/generators/typescript/sdk/versions.yml
index 74863357dbf4..b1880aa3bb9c 100644
--- a/generators/typescript/sdk/versions.yml
+++ b/generators/typescript/sdk/versions.yml
@@ -1,4 +1,12 @@
 # yaml-language-server: $schema=../../../fern-versions-yml.schema.json
+- version: 3.38.4
+  changelogEntry:
+    - summary: |
+        Update WebSocket `ConnectArgs` interface to type `allow-multiple: true` query parameters as `T | T[] | undefined` instead of `T | T[]` for consistency.
+      type: fix
+  createdAt: "2025-12-09"
+  irVersion: 62
+
 - version: 3.38.3
   changelogEntry:
     - summary: |