Backport: fix(ai): remove custom User-Agent header from chat transport (#13338)

vercel-ai-sdk[bot] · gr2m · claude · web-flow · commit 578615a7b45b · 2026-03-11T14:58:47.000Z
This is an automated backport of #13330 to the release-v6.0 branch. FYI @gr2m ## Related Issues Fixes #9256 Co-authored-by: Gregor Martynus <39992+gr2m@users.noreply.github.com> Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
diff --git a/.changeset/remove-useragent-usechat.md b/.changeset/remove-useragent-usechat.md
@@ -0,0 +1,5 @@
+---
+'ai': patch
+---
+
+Remove custom User-Agent header from HttpChatTransport to fix CORS preflight failures in Safari and Firefox
diff --git a/packages/ai/src/ui/http-chat-transport.test.ts b/packages/ai/src/ui/http-chat-transport.test.ts
@@ -148,7 +148,6 @@ describe('HttpChatTransport', () => {
       expect(server.calls[0].requestHeaders['x-test-header']).toBe(
         'test-value',
       );
-      expect(server.calls[0].requestUserAgent).toContain('ai-sdk/');
     });
 
     it('should include headers in the request when a function is provided', async () => {
@@ -179,7 +178,6 @@ describe('HttpChatTransport', () => {
       expect(server.calls[0].requestHeaders['x-test-header']).toBe(
         'test-value-fn',
       );
-      expect(server.calls[0].requestUserAgent).toContain('ai-sdk/');
     });
   });
 });
diff --git a/packages/ai/src/ui/http-chat-transport.ts b/packages/ai/src/ui/http-chat-transport.ts
@@ -3,13 +3,10 @@ import {
   Resolvable,
   normalizeHeaders,
   resolve,
-  withUserAgentSuffix,
-  getRuntimeEnvironmentUserAgent,
 } from '@ai-sdk/provider-utils';
 import { UIMessageChunk } from '../ui-message-stream/ui-message-chunks';
 import { ChatTransport } from './chat-transport';
 import { UIMessage } from './ui-messages';
-import { VERSION } from '../version';
 
 export type PrepareSendMessagesRequest<UI_MESSAGE extends UIMessage> = (
   options: {
@@ -193,14 +190,10 @@ export abstract class HttpChatTransport<UI_MESSAGE extends UIMessage>
 
     const response = await fetch(api, {
       method: 'POST',
-      headers: withUserAgentSuffix(
-        {
-          'Content-Type': 'application/json',
-          ...headers,
-        },
-        `ai-sdk/${VERSION}`,
-        getRuntimeEnvironmentUserAgent(),
-      ),
+      headers: {
+        'Content-Type': 'application/json',
+        ...headers,
+      },
       body: JSON.stringify(body),
       credentials,
       signal: abortSignal,
@@ -252,11 +245,7 @@ export abstract class HttpChatTransport<UI_MESSAGE extends UIMessage>
 
     const response = await fetch(api, {
       method: 'GET',
-      headers: withUserAgentSuffix(
-        headers,
-        `ai-sdk/${VERSION}`,
-        getRuntimeEnvironmentUserAgent(),
-      ),
+      headers,
       credentials,
     });
 

-Original file line number
+Diff line change
@@ @@ -0,0 +1,5 @@ @@
 +---
 +'ai': patch
 +---
++
 +Remove custom User-Agent header from HttpChatTransport to fix CORS preflight failures in Safari and Firefox