feat(ai-gateway): map custom LLM thought content

apps/web/src/app/api/openrouter/[...path]/route.test.ts

@@ -134,6 +134,7 @@ const provider = {
   apiUrl: 'https://openrouter.ai/api/v1',
   apiKey: 'test-key',
   supportedChatApis: ['chat_completions', 'responses', 'messages'],
+  responseTransforms: null,
   transformRequest: jest.fn(),
 } satisfies Provider;
 
@@ -291,7 +292,31 @@ describe('POST /api/openrouter/v1/chat/completions rules-engine actions', () =>
       expect.anything(),
       expect.anything(),
       expect.anything(),
-      expect.objectContaining({ vercel_request_id: 'iad1::iad1::request-id' })
+      expect.objectContaining({ vercel_request_id: 'iad1::iad1::request-id' }),
+      null
+    );
+  });
+
+  it('passes provider response transforms to the response rewriter', async () => {
+    const responseTransforms = { thoughtContentMapping: 'extra_content.flags.thought' };
+    mockedGetProvider.mockResolvedValue({
+      kind: 'provider',
+      provider: { ...provider, responseTransforms },
+      userByok: null,
+      bypassAccessCheck: false,
+    });
+    const { POST } = await import('./route');
+
+    const response = await POST(makeRequest(makeBody()) as never);
+
+    expect(response.status).toBe(200);
+    expect(mockedRewriteModelResponse).toHaveBeenCalledWith(
+      expect.anything(),
+      expect.anything(),
+      expect.anything(),
+      expect.anything(),
+      expect.anything(),
+      responseTransforms
     );
   });
 

apps/web/src/app/api/openrouter/[...path]/route.ts

@@ -1039,6 +1039,7 @@ export async function POST(request: NextRequest): Promise<NextResponseType<unkno
     effectiveModelIdLowerCased,
     effectiveProviderContext.provider.id,
     requestBodyParsed.kind,
-    requestLogging
+    requestLogging,
+    effectiveProviderContext.provider.responseTransforms
   );
 }

apps/web/src/lib/ai-gateway/experiments/build-direct-provider.test.ts

@@ -91,6 +91,56 @@ describe('custom LLM thought signature mapping configuration', () => {
   );
 });
 
+describe('custom LLM thought content mapping configuration', () => {
+  const config = {
+    internal_id: 'upstream-model',
+    base_url: 'https://llm.example.com/v1',
+  };
+
+  it('accepts a dot-separated property path', () => {
+    expect(
+      CustomLlmApiConfigSchema.safeParse({
+        ...config,
+        thought_content_mapping: 'extra_content.flags.thought',
+      }).success
+    ).toBe(true);
+  });
+
+  it.each(['', 'extra_content..thought', 'constructor.prototype.thought'])(
+    'rejects unsafe property path %p',
+    thought_content_mapping => {
+      expect(
+        CustomLlmApiConfigSchema.safeParse({ ...config, thought_content_mapping }).success
+      ).toBe(false);
+    }
+  );
+});
+
+describe('buildDirectProvider response transforms', () => {
+  it('exposes the thought content property path without other upstream configuration', () => {
+    const provider = buildDirectProvider('custom', ['chat_completions'], {
+      internal_id: 'upstream-model',
+      base_url: 'https://llm.example.com/v1',
+      api_key: 'test-key',
+      thought_content_mapping: 'extra_content.flags.thought',
+    });
+
+    expect(provider.responseTransforms).toEqual({
+      thoughtContentMapping: 'extra_content.flags.thought',
+    });
+  });
+
+  it('sets response transforms to null when no mapping is configured', () => {
+    const provider = buildDirectProvider('custom', ['chat_completions'], {
+      internal_id: 'upstream-model',
+      base_url: 'https://llm.example.com/v1',
+      api_key: 'test-key',
+    });
+
+    expect(provider.responseTransforms).toBeNull();
+  });
+});
+
 describe('buildDirectProvider thought signature mapping', () => {
   it('maps assistant tool-call signatures and removes camel-case transport fields', async () => {
     const request = makeRequest();

apps/web/src/lib/ai-gateway/experiments/build-direct-provider.ts

@@ -202,6 +202,9 @@ export function buildDirectProvider(
     apiUrl: upstream.base_url,
     apiKey: upstream.api_key,
     supportedChatApis,
+    responseTransforms: upstream.thought_content_mapping
+      ? { thoughtContentMapping: upstream.thought_content_mapping }
+      : null,
     async transformRequest(context) {
       if (upstream.remove_from_body) {
         const body = context.request.body as Record<string, unknown>;

apps/web/src/lib/ai-gateway/providers/get-provider.ts

@@ -80,6 +80,7 @@ async function checkDirectBYOK(
       apiUrl: directByok.base_url,
       apiKey: userByok[0].decryptedAPIKey,
       supportedChatApis: directByok.supported_chat_apis,
+      responseTransforms: null,
       async transformRequest(context) {
         context.request.body.model = directByokModel.id;
         directByok.transformRequest(context);

apps/web/src/lib/ai-gateway/providers/provider-definitions.ts

@@ -9,6 +9,7 @@ export default {
     apiUrl: 'https://openrouter.ai/api/v1',
     apiKey: getEnvVariable('OPENROUTER_API_KEY'),
     supportedChatApis: ['chat_completions', 'messages', 'responses'],
+    responseTransforms: null,
     async transformRequest() {},
   },
   ALIBABA: {
@@ -17,6 +18,7 @@ export default {
     apiKey: getEnvVariable('ALIBABA_API_KEY'),
     // Prompt caching is not supported on the responses API for Alibaba; enabling it is therefore dangerous.
     supportedChatApis: ['chat_completions' /*, 'responses'*/],
+    responseTransforms: null,
     async transformRequest(context) {
       context.request.body.enable_thinking = !isReasoningExplicitlyDisabled(context.request);
     },
@@ -27,6 +29,7 @@ export default {
     apiKey: getEnvVariable('BYTEDANCE_API_KEY'),
     // Prompt caching is not supported on the responses API for Bytedance; enabling it is therefore dangerous.
     supportedChatApis: ['chat_completions' /*, 'responses'*/],
+    responseTransforms: null,
     async transformRequest(context) {
       if (!isReasoningExplicitlyDisabled(context.request)) {
         context.request.body.thinking = { type: 'enabled' };
@@ -49,6 +52,7 @@ export default {
     apiUrl: 'https://api.withmartian.com/v1',
     apiKey: getEnvVariable('MARTIAN_API_KEY'),
     supportedChatApis: ['chat_completions', 'responses', 'messages'],
+    responseTransforms: null,
     async transformRequest(context) {
       delete context.request.body.provider;
     },
@@ -58,13 +62,15 @@ export default {
     apiUrl: 'https://api.mistral.ai/v1',
     apiKey: getEnvVariable('MISTRAL_API_KEY'),
     supportedChatApis: [],
+    responseTransforms: null,
     async transformRequest() {},
   },
   STREAMLAKE: {
     id: 'streamlake',
     apiUrl: 'https://vanchin.streamlake.ai/api/gateway/v1/endpoints',
     apiKey: getEnvVariable('STREAMLAKE_API_KEY'),
     supportedChatApis: ['chat_completions'],
+    responseTransforms: null,
     async transformRequest(context) {
       delete context.request.body.provider;
     },
@@ -74,6 +80,7 @@ export default {
     apiUrl: 'https://ai-gateway.vercel.sh/v1',
     apiKey: getEnvVariable('VERCEL_AI_GATEWAY_API_KEY'),
     supportedChatApis: ['chat_completions', 'messages', 'responses'],
+    responseTransforms: null,
     async transformRequest(context) {
       await applyVercelSettings(context.model, context.request, context.userByok);
     },

apps/web/src/lib/ai-gateway/providers/types.ts

@@ -35,10 +35,15 @@ export type TransformRequestContext = {
 
 export type GatewayChatApiKind = GatewayRequest['kind'];
 
+export type ProviderResponseTransforms = {
+  thoughtContentMapping: string | null;
+};
+
 export type Provider = {
   id: ProviderId;
   apiUrl: string;
   apiKey: string;
   supportedChatApis: ReadonlyArray<GatewayChatApiKind>;
+  responseTransforms: ProviderResponseTransforms | null;
   transformRequest(context: TransformRequestContext): Promise<void>;
 };

apps/web/src/lib/ai-gateway/providers/upstream-request.generation.test.ts

@@ -20,6 +20,7 @@ const provider: Provider = {
   apiUrl: 'https://openrouter.example/api/v1',
   apiKey: 'test-api-key',
   supportedChatApis: [],
+  responseTransforms: null,
   transformRequest: async () => {},
 };