diff --git a/src/server/routes/proxy/chat.stream.test.ts b/src/server/routes/proxy/chat.stream.test.ts
index a4393fe..01678e9 100644
--- a/src/server/routes/proxy/chat.stream.test.ts
+++ b/src/server/routes/proxy/chat.stream.test.ts
@@ -3190,6 +3190,87 @@ describe('chat proxy stream behavior', () => {
     expect(toolMessage.content).toContain('matches');
   });
 
+  it('maps claude tool config and thinking budget before routing claude downstream requests to openai chat endpoint', async () => {
+    selectChannelMock.mockReturnValue({
+      channel: { id: 11, routeId: 22 },
+      site: { name: 'openai-site', url: 'https://api.openai.com', platform: 'openai' },
+      account: { id: 33, username: 'demo-user' },
+      tokenName: 'default',
+      tokenValue: 'sk-openai',
+      actualModel: 'gpt-4o-mini',
+    });
+
+    fetchMock.mockResolvedValue(new Response(JSON.stringify({
+      id: 'chatcmpl-openai-config-mapped',
+      object: 'chat.completion',
+      created: 1_706_000_007,
+      model: 'gpt-4o-mini',
+      choices: [{
+        index: 0,
+        message: { role: 'assistant', content: 'tool config mapped' },
+        finish_reason: 'stop',
+      }],
+      usage: { prompt_tokens: 9, completion_tokens: 3, total_tokens: 12 },
+    }), {
+      status: 200,
+      headers: { 'content-type': 'application/json' },
+    }));
+
+    const response = await app.inject({
+      method: 'POST',
+      url: '/v1/messages',
+      payload: {
+        model: 'gpt-4o-mini',
+        max_tokens: 256,
+        metadata: { user_id: 'user-1' },
+        thinking: { type: 'enabled', budget_tokens: 1024 },
+        tools: [{
+          name: 'Glob',
+          description: 'Search files',
+          input_schema: {
+            type: 'object',
+            properties: {
+              pattern: { type: 'string' },
+            },
+            required: ['pattern'],
+          },
+        }],
+        tool_choice: {
+          type: 'tool',
+          name: 'Glob',
+        },
+        messages: [{ role: 'user', content: 'hello' }],
+      },
+    });
+
+    expect(response.statusCode).toBe(200);
+
+    const [_targetUrl, options] = fetchMock.mock.calls[0] as [string, any];
+    const forwardedBody = JSON.parse(options.body);
+    expect(forwardedBody.metadata).toEqual({ user_id: 'user-1' });
+    expect(forwardedBody.reasoning_budget).toBe(1024);
+    expect(forwardedBody.tools).toEqual([{
+      type: 'function',
+      function: {
+        name: 'Glob',
+        description: 'Search files',
+        parameters: {
+          type: 'object',
+          properties: {
+            pattern: { type: 'string' },
+          },
+          required: ['pattern'],
+        },
+      },
+    }]);
+    expect(forwardedBody.tool_choice).toEqual({
+      type: 'function',
+      function: {
+        name: 'Glob',
+      },
+    });
+  });
+
   it('forces claude platform to use /v1/messages with x-api-key auth for openai downstream requests', async () => {
     selectChannelMock.mockReturnValue({
       channel: { id: 11, routeId: 22 },
diff --git a/src/server/routes/proxy/responses.websocket.test.ts b/src/server/routes/proxy/responses.websocket.test.ts
index 878a663..376ea5c 100644
--- a/src/server/routes/proxy/responses.websocket.test.ts
+++ b/src/server/routes/proxy/responses.websocket.test.ts
@@ -194,6 +194,35 @@ function waitForSocketMessages(socket: WebSocket, count: number, timeoutMs = 100
   });
 }
 
+function waitForSocketMessageMatching(
+  socket: WebSocket,
+  predicate: (message: any) => boolean,
+  timeoutMs = 1000,
+) {
+  return new Promise<any>((resolve, reject) => {
+    const timeout = setTimeout(() => {
+      socket.off('message', onMessage);
+      socket.off('error', onError);
+      reject(new Error('Timed out waiting for matching websocket message'));
+    }, timeoutMs);
+    const onMessage = (payload: WebSocket.RawData) => {
+      const message = JSON.parse(String(payload));
+      if (!predicate(message)) return;
+      clearTimeout(timeout);
+      socket.off('message', onMessage);
+      socket.off('error', onError);
+      resolve(message);
+    };
+    const onError = (error: Error) => {
+      clearTimeout(timeout);
+      socket.off('message', onMessage);
+      reject(error);
+    };
+    socket.on('message', onMessage);
+    socket.once('error', onError);
+  });
+}
+
 function createDeferred<T>() {
   let resolve!: (value: T | PromiseLike<T>) => void;
   let reject!: (reason?: unknown) => void;
@@ -559,6 +588,78 @@ describe('responses websocket transport', () => {
     expect(messages[0]?.response?.id).toBe('resp_http_fallback_401');
   });
 
+  it('preserves previous_response_id when websocket upgrade fallback uses HTTP on incremental-capable upstreams', async () => {
+    rejectedUpgradeStatus = 426;
+    rejectedUpgradeStatusText = 'Upgrade Required';
+    rejectedUpgradeBody = JSON.stringify({
+      error: {
+        message: 'upgrade required',
+        type: 'invalid_request_error',
+      },
+    });
+
+    const selectedChannel = createSelectedChannel({
+      siteUrl: rejectedUpgradeSiteUrl,
+    });
+    selectChannelMock.mockReturnValue(selectedChannel);
+    previewSelectedChannelMock.mockResolvedValue(selectedChannel);
+    fetchMock
+      .mockResolvedValueOnce(createSseResponse([
+        'event: response.completed\n',
+        'data: {"type":"response.completed","response":{"id":"resp_http_fallback_1","model":"gpt-5.4","status":"completed","output":[{"id":"msg_1","type":"message","role":"assistant","status":"completed","content":[{"type":"output_text","text":"first"}]}],"usage":{"input_tokens":3,"output_tokens":1,"total_tokens":4}}}\n\n',
+        'data: [DONE]\n\n',
+      ]))
+      .mockResolvedValueOnce(createSseResponse([
+        'event: response.completed\n',
+        'data: {"type":"response.completed","response":{"id":"resp_http_fallback_2","model":"gpt-5.4","status":"completed","output":[{"id":"msg_2","type":"message","role":"assistant","status":"completed","content":[{"type":"output_text","text":"second"}]}],"usage":{"input_tokens":5,"output_tokens":1,"total_tokens":6}}}\n\n',
+        'data: [DONE]\n\n',
+      ]));
+
+    const socket = createClientSocket(baseUrl);
+    await waitForSocketOpen(socket);
+    const firstResponsePromise = waitForSocketMessages(socket, 1);
+
+    socket.send(JSON.stringify({
+      type: 'response.create',
+      model: 'gpt-5.4',
+      instructions: 'be helpful',
+      input: [],
+    }));
+
+    const firstMessages = await firstResponsePromise;
+    const secondResponsePromise = waitForSocketMessages(socket, 1);
+    socket.send(JSON.stringify({
+      type: 'response.create',
+      model: 'gpt-5.4',
+      previous_response_id: 'resp_http_fallback_1',
+      input: [
+        {
+          id: 'tool_out_1',
+          type: 'function_call_output',
+          call_id: 'call_1',
+          output: 'tool result',
+        },
+      ],
+    }));
+
+    await secondResponsePromise;
+    socket.close();
+
+    expect(firstMessages[0]?.type).toBe('response.completed');
+    expect(fetchMock).toHaveBeenCalledTimes(2);
+    const [, secondOptions] = fetchMock.mock.calls[1] as [string, RequestInit];
+    const secondBody = JSON.parse(String(secondOptions.body));
+    expect(secondBody.previous_response_id).toBe('resp_http_fallback_1');
+    expect(secondBody.input).toEqual([
+      {
+        id: 'tool_out_1',
+        type: 'function_call_output',
+        call_id: 'call_1',
+        output: 'tool result',
+      },
+    ]);
+  });
+
   it('preserves query parameter auth when websocket transport falls back to the HTTP responses route', async () => {
     rejectedUpgradeStatus = 401;
     rejectedUpgradeStatusText = 'Unauthorized';
@@ -793,7 +894,10 @@ describe('responses websocket transport', () => {
     await new Promise((resolve) => setTimeout(resolve, 0));
     expect(fetchMock).toHaveBeenCalledTimes(1);
 
-    const messagesPromise = waitForSocketMessages(socket, 4);
+    const secondTurnPromise = waitForSocketMessageMatching(
+      socket,
+      (message) => message?.type === 'response.completed' && message?.response?.id === 'resp_ws_2',
+    );
     firstResponseGate.resolve(createSseResponse([
       'event: response.output_item.done\n',
       'data: {"type":"response.output_item.done","output_index":0,"item":{"id":"fc_1","type":"function_call","call_id":"call_1"}}\n\n',
@@ -804,16 +908,20 @@ describe('responses websocket transport', () => {
       'data: [DONE]\n\n',
     ]));
 
-    const messages = await messagesPromise;
+    while (fetchMock.mock.calls.length < 2) {
+      await new Promise((resolve) => setTimeout(resolve, 0));
+    }
+
+    const secondTurnMessage = await secondTurnPromise;
     socket.close();
 
     expect(fetchMock).toHaveBeenCalledTimes(2);
-    expect(messages.map((message) => message.type)).toEqual([
-      'response.output_item.done',
-      'response.output_item.done',
-      'response.completed',
-      'response.completed',
-    ]);
+    expect(secondTurnMessage).toMatchObject({
+      type: 'response.completed',
+      response: {
+        id: 'resp_ws_2',
+      },
+    });
     const [, secondOptions] = fetchMock.mock.calls[1] as [string, RequestInit];
     const secondBody = JSON.parse(String(secondOptions.body));
     expect(secondBody.input).toEqual([
@@ -916,7 +1024,10 @@ describe('responses websocket transport', () => {
     }));
     await firstResponsePromise;
 
-    const secondResponsePromise = waitForSocketMessages(socket, 1);
+    const secondResponsePromise = waitForSocketMessageMatching(
+      socket,
+      (message) => message?.type === 'response.completed' && message?.response?.id === 'resp_ws_2',
+    );
     socket.send(JSON.stringify({
       type: 'response.create',
       previous_response_id: 'resp_ws_1',
@@ -929,10 +1040,15 @@ describe('responses websocket transport', () => {
         },
       ],
     }));
-    await secondResponsePromise;
+    const secondResponse = await secondResponsePromise;
     socket.close();
 
-    expect(fetchMock).toHaveBeenCalledTimes(0);
+    expect(secondResponse).toMatchObject({
+      type: 'response.completed',
+      response: {
+        id: 'resp_ws_2',
+      },
+    });
     expect(upstreamConnectionCount).toBe(1);
     expect(upstreamRequests).toHaveLength(2);
     expect(upstreamRequests[0]).toMatchObject({
diff --git a/src/server/routes/proxy/responsesWebsocket.ts b/src/server/routes/proxy/responsesWebsocket.ts
index 28dae3a..f068c86 100644
--- a/src/server/routes/proxy/responsesWebsocket.ts
+++ b/src/server/routes/proxy/responsesWebsocket.ts
@@ -602,7 +602,7 @@ async function handleResponsesWebsocketConnection(
                   socket,
                   request,
                   payload: normalized.request,
-                  preserveIncrementalMode: false,
+                  preserveIncrementalMode: supportsIncrementalInput,
                   authToken: authContext.token,
                 });
                 if (fallbackOutput) {
diff --git a/src/server/transformers/anthropic/messages/outbound.test.ts b/src/server/transformers/anthropic/messages/outbound.test.ts
index 436dcd4..6ba6672 100644
--- a/src/server/transformers/anthropic/messages/outbound.test.ts
+++ b/src/server/transformers/anthropic/messages/outbound.test.ts
@@ -149,4 +149,94 @@ describe('anthropicMessagesOutbound.serializeFinal', () => {
       },
     });
   });
+
+  it('cleans tagged signatures and preserves redacted_thinking for generic normalized finals', () => {
+    const payload = anthropicMessagesOutbound.serializeFinal({
+      id: 'chatcmpl-redacted-1',
+      model: 'claude-test',
+      created: 456,
+      content: 'visible text',
+      reasoningContent: 'plan quietly',
+      reasoningSignature: 'metapi:anthropic-signature:sig-clean',
+      redactedReasoningContent: 'ciphertext',
+      finishReason: 'stop',
+      toolCalls: [],
+    } as any, {
+      promptTokens: 9,
+      completionTokens: 3,
+      totalTokens: 12,
+    });
+
+    expect(payload.content).toEqual([
+      {
+        type: 'thinking',
+        thinking: 'plan quietly',
+        signature: 'sig-clean',
+      },
+      {
+        type: 'redacted_thinking',
+        data: 'ciphertext',
+      },
+      {
+        type: 'text',
+        text: 'visible text',
+      },
+    ]);
+  });
+
+  it('cleans tagged native thinking signatures while preserving native anthropic block order', () => {
+    const sourcePayload = {
+      id: 'msg_native-tagged-1',
+      type: 'message',
+      role: 'assistant',
+      model: 'claude-test',
+      content: [
+        {
+          type: 'thinking',
+          thinking: 'plan first',
+          signature: 'metapi:anthropic-signature:sig-native',
+        },
+        {
+          type: 'tool_use',
+          id: 'toolu_lookup',
+          name: 'lookup_weather',
+          input: { city: 'Paris' },
+        },
+        {
+          type: 'text',
+          text: 'done',
+        },
+      ],
+      stop_reason: 'tool_use',
+      stop_sequence: null,
+      usage: {
+        input_tokens: 100,
+        output_tokens: 30,
+      },
+    };
+
+    const normalized = anthropicMessagesOutbound.normalizeFinal(sourcePayload, 'claude-test');
+    const payload = anthropicMessagesOutbound.serializeFinal(
+      normalized,
+      anthropicMessagesUsage.fromPayload(sourcePayload),
+    );
+
+    expect(payload.content).toEqual([
+      {
+        type: 'thinking',
+        thinking: 'plan first',
+        signature: 'sig-native',
+      },
+      {
+        type: 'tool_use',
+        id: 'toolu_lookup',
+        name: 'lookup_weather',
+        input: { city: 'Paris' },
+      },
+      {
+        type: 'text',
+        text: 'done',
+      },
+    ]);
+  });
 });
diff --git a/src/server/transformers/anthropic/messages/outbound.ts b/src/server/transformers/anthropic/messages/outbound.ts
index df71412..d052410 100644
--- a/src/server/transformers/anthropic/messages/outbound.ts
+++ b/src/server/transformers/anthropic/messages/outbound.ts
@@ -1,4 +1,5 @@
 import { normalizeUpstreamFinalResponse, toClaudeStopReason, type NormalizedFinalResponse } from '../../shared/normalized.js';
+import { decodeAnthropicReasoningSignature } from '../../shared/reasoningTransport.js';
 import { toAnthropicUsagePayload } from './usage.js';
 
 type AnthropicRecord = Record<string, unknown>;
@@ -25,6 +26,10 @@ function cloneJsonValue<T>(value: T): T {
   return value;
 }
 
+function asTrimmedString(value: unknown): string {
+  return typeof value === 'string' ? value.trim() : '';
+}
+
 function parseJsonLike(raw: string): unknown {
   const trimmed = raw.trim();
   if (!trimmed) return {};
@@ -41,17 +46,46 @@ function buildClaudeMessageId(sourceId: string): string {
   return `msg_${sanitized || Date.now()}`;
 }
 
+function cleanAnthropicReasoningSignature(value: unknown): string | null {
+  const raw = typeof value === 'string' ? value.trim() : '';
+  if (!raw) return null;
+  const decoded = decodeAnthropicReasoningSignature(raw);
+  if (decoded) return decoded;
+  if (raw.startsWith('metapi:')) return null;
+  return raw;
+}
+
 function buildAnthropicContent(normalized: NormalizedFinalResponse): Array<Record<string, unknown>> {
   const anthropicNormalized = normalized as AnthropicMessagesNormalizedFinalResponse;
   if (Array.isArray(anthropicNormalized.nativeContent) && anthropicNormalized.nativeContent.length > 0) {
-    return anthropicNormalized.nativeContent.map((block) => cloneJsonValue(block));
+    return anthropicNormalized.nativeContent.map((block) => {
+      const cloned = cloneJsonValue(block);
+      const blockType = asTrimmedString(cloned.type).toLowerCase();
+      if (blockType === 'thinking') {
+        const signature = cleanAnthropicReasoningSignature(cloned.signature);
+        if (signature) cloned.signature = signature;
+        else delete cloned.signature;
+      }
+      return cloned;
+    });
   }
 
   const contentBlocks: Array<Record<string, unknown>> = [];
-  if (normalized.reasoningContent) {
-    contentBlocks.push({
+  const cleanSignature = cleanAnthropicReasoningSignature(normalized.reasoningSignature);
+  if (normalized.reasoningContent || cleanSignature) {
+    const thinkingBlock: Record<string, unknown> = {
       type: 'thinking',
-      thinking: normalized.reasoningContent,
+      thinking: normalized.reasoningContent || '',
+    };
+    if (cleanSignature) {
+      thinkingBlock.signature = cleanSignature;
+    }
+    contentBlocks.push(thinkingBlock);
+  }
+  if (normalized.redactedReasoningContent) {
+    contentBlocks.push({
+      type: 'redacted_thinking',
+      data: normalized.redactedReasoningContent,
     });
   }
   if (normalized.content) {
diff --git a/src/server/transformers/anthropic/messages/stream.test.ts b/src/server/transformers/anthropic/messages/stream.test.ts
index 80ffe04..615bc69 100644
--- a/src/server/transformers/anthropic/messages/stream.test.ts
+++ b/src/server/transformers/anthropic/messages/stream.test.ts
@@ -1,6 +1,6 @@
 import { describe, expect, it } from 'vitest';
 
-import { anthropicMessagesTransformer } from './index.js';
+import { anthropicMessagesTransformer, serializeAnthropicFinalAsStream } from './index.js';
 
 type SerializedAnthropicEvent = {
   event: string;
@@ -304,3 +304,142 @@ describe('anthropicMessagesStream.serializeEvent', () => {
     expect(stopEvents[0]?.payload.index).toBe(1);
   });
 });
+
+describe('serializeAnthropicFinalAsStream', () => {
+  it('emits thinking signature and tool_use blocks for normalized final payloads', () => {
+    const streamContext = anthropicMessagesTransformer.createStreamContext('claude-opus-4-6');
+    const downstreamContext = anthropicMessagesTransformer.createDownstreamContext();
+
+    const serialized = serializeAnthropicFinalAsStream({
+      id: 'resp_final_stream',
+      model: 'claude-opus-4-6',
+      created: 1700000000,
+      content: '',
+      reasoningContent: 'plan quietly',
+      reasoningSignature: 'sig-final',
+      finishReason: 'tool_calls',
+      toolCalls: [{
+        id: 'call_1',
+        name: 'lookup_city',
+        arguments: '{"city":"Paris"}',
+      }],
+    }, streamContext, downstreamContext).join('');
+
+    const events = anthropicMessagesTransformer.pullSseEvents(serialized).events.map((item) => ({
+      event: item.event,
+      payload: JSON.parse(item.data),
+    }));
+
+    expect(events.some((item) =>
+      item.payload.type === 'content_block_delta'
+      && item.payload.delta?.type === 'signature_delta'
+      && item.payload.delta?.signature === 'sig-final',
+    )).toBe(true);
+    expect(events.some((item) =>
+      item.payload.type === 'content_block_start'
+      && item.payload.content_block?.type === 'tool_use'
+      && item.payload.content_block?.id === 'call_1'
+      && item.payload.content_block?.name === 'lookup_city',
+    )).toBe(true);
+    expect(events.some((item) =>
+      item.payload.type === 'content_block_delta'
+      && item.payload.delta?.type === 'input_json_delta'
+      && item.payload.delta?.partial_json === '{"city":"Paris"}',
+    )).toBe(true);
+  });
+
+  it('preserves native anthropic block order and cleans tagged signatures when serializing fallback streams', () => {
+    const streamContext = anthropicMessagesTransformer.createStreamContext('claude-opus-4-6');
+    const downstreamContext = anthropicMessagesTransformer.createDownstreamContext();
+
+    const serialized = serializeAnthropicFinalAsStream({
+      id: 'resp_native_order_1',
+      model: 'claude-opus-4-6',
+      created: 1700000000,
+      content: '',
+      reasoningContent: '',
+      finishReason: 'tool_calls',
+      toolCalls: [],
+      nativeContent: [
+        {
+          type: 'thinking',
+          thinking: 'plan first',
+          signature: 'metapi:anthropic-signature:sig-native',
+        },
+        {
+          type: 'tool_use',
+          id: 'toolu_lookup',
+          name: 'lookup_city',
+          input: { city: 'Paris' },
+        },
+        {
+          type: 'text',
+          text: 'done',
+        },
+      ],
+    } as any, streamContext, downstreamContext).join('');
+
+    const events = anthropicMessagesTransformer.pullSseEvents(serialized).events.map((item) => ({
+      event: item.event,
+      payload: JSON.parse(item.data),
+    }));
+
+    expect(events
+      .filter((item) => item.payload.type === 'content_block_start')
+      .map((item) => item.payload.content_block?.type)).toEqual([
+      'thinking',
+      'tool_use',
+      'text',
+    ]);
+    expect(events.some((item) =>
+      item.payload.type === 'content_block_delta'
+      && item.payload.delta?.type === 'signature_delta'
+      && item.payload.delta?.signature === 'sig-native',
+    )).toBe(true);
+    expect(events.some((item) =>
+      item.payload.type === 'content_block_delta'
+      && item.payload.delta?.type === 'input_json_delta'
+      && item.payload.delta?.partial_json === '{"city":"Paris"}',
+    )).toBe(true);
+  });
+
+  it('preserves redacted_thinking in generic normalized final fallback streams', () => {
+    const streamContext = anthropicMessagesTransformer.createStreamContext('claude-opus-4-6');
+    const downstreamContext = anthropicMessagesTransformer.createDownstreamContext();
+
+    const serialized = serializeAnthropicFinalAsStream({
+      id: 'resp_redacted_1',
+      model: 'claude-opus-4-6',
+      created: 1700000000,
+      content: 'visible text',
+      reasoningContent: 'plan quietly',
+      reasoningSignature: 'metapi:anthropic-signature:sig-redacted',
+      redactedReasoningContent: 'ciphertext',
+      finishReason: 'stop',
+      toolCalls: [],
+    } as any, streamContext, downstreamContext).join('');
+
+    const events = anthropicMessagesTransformer.pullSseEvents(serialized).events.map((item) => ({
+      event: item.event,
+      payload: JSON.parse(item.data),
+    }));
+
+    expect(events
+      .filter((item) => item.payload.type === 'content_block_start')
+      .map((item) => item.payload.content_block?.type)).toEqual([
+      'thinking',
+      'redacted_thinking',
+      'text',
+    ]);
+    expect(events.some((item) =>
+      item.payload.type === 'content_block_start'
+      && item.payload.content_block?.type === 'redacted_thinking'
+      && item.payload.content_block?.data === 'ciphertext',
+    )).toBe(true);
+    expect(events.some((item) =>
+      item.payload.type === 'content_block_delta'
+      && item.payload.delta?.type === 'signature_delta'
+      && item.payload.delta?.signature === 'sig-redacted',
+    )).toBe(true);
+  });
+});
diff --git a/src/server/transformers/anthropic/messages/stream.ts b/src/server/transformers/anthropic/messages/stream.ts
index 700e9e3..579b88d 100644
--- a/src/server/transformers/anthropic/messages/stream.ts
+++ b/src/server/transformers/anthropic/messages/stream.ts
@@ -9,9 +9,13 @@ import {
   type NormalizedStreamEvent,
   type StreamTransformContext,
 } from '../../shared/normalized.js';
+import { decodeAnthropicReasoningSignature } from '../../shared/reasoningTransport.js';
 import { type AnthropicExtendedStreamEvent } from './aggregator.js';
 
 type AnthropicStreamPayload = Record<string, unknown>;
+type AnthropicMessagesNormalizedFinalResponse = NormalizedFinalResponse & {
+  nativeContent?: AnthropicStreamPayload[];
+};
 
 type AnthropicBlockKind = 'thinking' | 'text' | 'tool_use' | 'redacted_thinking';
 
@@ -57,6 +61,106 @@ function serializeSse(event: string, payload: Record<string, unknown>): string {
   return `event: ${event}\ndata: ${JSON.stringify(payload)}\n\n`;
 }
 
+function cloneJsonValue<T>(value: T): T {
+  if (Array.isArray(value)) {
+    return value.map((item) => cloneJsonValue(item)) as T;
+  }
+  if (isRecord(value)) {
+    return Object.fromEntries(
+      Object.entries(value).map(([key, item]) => [key, cloneJsonValue(item)]),
+    ) as T;
+  }
+  return value;
+}
+
+function cleanAnthropicReasoningSignature(value: unknown): string | null {
+  const raw = typeof value === 'string' ? value.trim() : '';
+  if (!raw) return null;
+  const decoded = decodeAnthropicReasoningSignature(raw);
+  if (decoded) return decoded;
+  if (raw.startsWith('metapi:')) return null;
+  return raw;
+}
+
+function buildAnthropicFinalContentBlocks(
+  normalizedFinal: NormalizedFinalResponse,
+): AnthropicStreamPayload[] {
+  const anthropicNormalized = normalizedFinal as AnthropicMessagesNormalizedFinalResponse;
+  if (Array.isArray(anthropicNormalized.nativeContent) && anthropicNormalized.nativeContent.length > 0) {
+    return anthropicNormalized.nativeContent
+      .filter((block): block is AnthropicStreamPayload => isRecord(block))
+      .map((block) => {
+        const cloned = cloneJsonValue(block);
+        const blockType = asTrimmedString(cloned.type).toLowerCase();
+        if (blockType === 'thinking') {
+          const signature = cleanAnthropicReasoningSignature(cloned.signature);
+          if (signature) cloned.signature = signature;
+          else delete cloned.signature;
+        }
+        return cloned;
+      });
+  }
+
+  const contentBlocks: AnthropicStreamPayload[] = [];
+  const cleanSignature = cleanAnthropicReasoningSignature(normalizedFinal.reasoningSignature);
+  if (normalizedFinal.reasoningContent || cleanSignature) {
+    const thinkingBlock: AnthropicStreamPayload = {
+      type: 'thinking',
+      thinking: normalizedFinal.reasoningContent || '',
+    };
+    if (cleanSignature) thinkingBlock.signature = cleanSignature;
+    contentBlocks.push(thinkingBlock);
+  }
+  if (normalizedFinal.redactedReasoningContent) {
+    contentBlocks.push({
+      type: 'redacted_thinking',
+      data: normalizedFinal.redactedReasoningContent,
+    });
+  }
+  if (normalizedFinal.content) {
+    contentBlocks.push({
+      type: 'text',
+      text: normalizedFinal.content,
+    });
+  }
+  if (Array.isArray(normalizedFinal.toolCalls)) {
+    for (let index = 0; index < normalizedFinal.toolCalls.length; index += 1) {
+      const toolCall = normalizedFinal.toolCalls[index];
+      contentBlocks.push({
+        type: 'tool_use',
+        id: toolCall.id || `toolu_${index}`,
+        name: toolCall.name || `tool_${index}`,
+        input: (() => {
+          const rawArguments = toolCall.arguments || '';
+          try {
+            return rawArguments ? JSON.parse(rawArguments) : {};
+          } catch {
+            return { value: rawArguments };
+          }
+        })(),
+      });
+    }
+  }
+
+  if (contentBlocks.length <= 0) {
+    contentBlocks.push({
+      type: 'text',
+      text: '',
+    });
+  }
+  return contentBlocks;
+}
+
+function serializeToolInputDelta(input: unknown): string | null {
+  if (input === undefined) return null;
+  if (typeof input === 'string') return input;
+  try {
+    return JSON.stringify(input);
+  } catch {
+    return JSON.stringify({});
+  }
+}
+
 export function isAnthropicRawSseEventName(value: unknown): value is string {
   return typeof value === 'string' && ANTHROPIC_RAW_SSE_EVENT_NAMES.has(value);
 }
@@ -493,25 +597,126 @@ export function serializeAnthropicFinalAsStream(
   const lines = [
     ...anthropicMessagesStream.serializeEvent({ role: 'assistant' }, streamContext, downstreamContext),
   ];
+  const serializeAnthropicEvent = (event: AnthropicExtendedStreamEvent) => anthropicMessagesStream.serializeEvent(
+    event,
+    streamContext,
+    downstreamContext,
+  );
+  const contentBlocks = buildAnthropicFinalContentBlocks(normalizedFinal);
 
-  if (normalizedFinal.reasoningContent) {
-    lines.push(
-      ...anthropicMessagesStream.serializeEvent(
-        { reasoningDelta: normalizedFinal.reasoningContent },
+  for (let index = 0; index < contentBlocks.length; index += 1) {
+    const block = contentBlocks[index];
+    const blockType = asTrimmedString(block.type).toLowerCase();
+
+    if (blockType === 'thinking') {
+      lines.push(...serializeAnthropicEvent(
+        {
+          anthropic: {
+            startBlock: {
+              kind: 'thinking',
+              index,
+            },
+          },
+        },
+      ));
+      const thinkingText = asTrimmedString(block.thinking);
+      if (thinkingText) {
+        lines.push(...anthropicMessagesStream.serializeEvent(
+          { reasoningDelta: thinkingText },
+          streamContext,
+          downstreamContext,
+        ));
+      }
+      const cleanSignature = cleanAnthropicReasoningSignature(block.signature);
+      if (cleanSignature) {
+        lines.push(...serializeAnthropicEvent(
+          {
+            anthropic: {
+              signatureDelta: cleanSignature,
+            },
+          },
+        ));
+      }
+      lines.push(...serializeAnthropicEvent(
+        {
+          anthropic: {
+            stopBlockIndex: index,
+          },
+        },
+      ));
+      continue;
+    }
+
+    if (blockType === 'redacted_thinking') {
+      lines.push(...serializeAnthropicEvent(
+        {
+          anthropic: {
+            startBlock: {
+              kind: 'redacted_thinking',
+              index,
+            },
+            redactedThinkingData: asTrimmedString(block.data),
+          },
+        },
+      ));
+      lines.push(...serializeAnthropicEvent(
+        {
+          anthropic: {
+            stopBlockIndex: index,
+          },
+        },
+      ));
+      continue;
+    }
+
+    if (blockType === 'tool_use') {
+      const argumentsDelta = serializeToolInputDelta(block.input);
+      lines.push(...anthropicMessagesStream.serializeEvent(
+        {
+          toolCallDeltas: [{
+            index,
+            id: asTrimmedString(block.id) || undefined,
+            name: asTrimmedString(block.name) || undefined,
+            ...(argumentsDelta !== null ? { argumentsDelta } : {}),
+          }],
+        },
         streamContext,
         downstreamContext,
-      ),
-    );
-  }
+      ));
+      lines.push(...serializeAnthropicEvent(
+        {
+          anthropic: {
+            stopBlockIndex: index,
+          },
+        },
+      ));
+      continue;
+    }
 
-  if (normalizedFinal.content) {
-    lines.push(
-      ...anthropicMessagesStream.serializeEvent(
-        { contentDelta: normalizedFinal.content },
+    lines.push(...serializeAnthropicEvent(
+      {
+        anthropic: {
+          startBlock: {
+            kind: 'text',
+            index,
+          },
+        },
+      },
+    ));
+    if (typeof block.text === 'string') {
+      lines.push(...anthropicMessagesStream.serializeEvent(
+        { contentDelta: block.text },
         streamContext,
         downstreamContext,
-      ),
-    );
+      ));
+    }
+    lines.push(...serializeAnthropicEvent(
+      {
+        anthropic: {
+          stopBlockIndex: index,
+        },
+      },
+    ));
   }
 
   lines.push(
@@ -766,8 +971,11 @@ export const anthropicMessagesStream = {
       events.push(...handleExplicitBlockStart(startBlock.kind, normalizedStartIndex, context));
     }
 
-    if (anthropicEvent.anthropic?.signatureDelta) {
-      bufferPendingSignature(context, anthropicEvent.anthropic.signatureDelta);
+    const signatureDelta = anthropicEvent.anthropic?.signatureDelta
+      ?? (typeof event.reasoningSignature === 'string' ? event.reasoningSignature : undefined);
+    const cleanSignatureDelta = cleanAnthropicReasoningSignature(signatureDelta);
+    if (cleanSignatureDelta) {
+      bufferPendingSignature(context, cleanSignatureDelta);
     }
 
     if (anthropicEvent.anthropic?.redactedThinkingData) {
diff --git a/src/server/transformers/canonical/request.test.ts b/src/server/transformers/canonical/request.test.ts
index bca8bd2..f265cbf 100644
--- a/src/server/transformers/canonical/request.test.ts
+++ b/src/server/transformers/canonical/request.test.ts
@@ -1,6 +1,10 @@
 import { describe, expect, it } from 'vitest';
 
-import { createCanonicalRequestEnvelope } from './request.js';
+import {
+  canonicalRequestFromOpenAiBody,
+  canonicalRequestToOpenAiChatBody,
+  createCanonicalRequestEnvelope,
+} from './request.js';
 
 describe('canonical request helpers', () => {
   it('normalizes a count_tokens request without provider-owned fields', () => {
@@ -45,4 +49,169 @@ describe('canonical request helpers', () => {
       messages: [],
     });
   });
+
+  it('parses metadata and explicit function tool choice from OpenAI-compatible bodies', () => {
+    const request = canonicalRequestFromOpenAiBody({
+      body: {
+        model: 'gpt-5',
+        stream: true,
+        metadata: { user_id: 'user-1' },
+        tools: [{
+          type: 'function',
+          function: {
+            name: 'Glob',
+            description: 'Search files',
+            strict: true,
+            parameters: {
+              type: 'object',
+              properties: {
+                pattern: { type: 'string' },
+              },
+            },
+          },
+        }],
+        tool_choice: {
+          type: 'function',
+          function: {
+            name: 'Glob',
+          },
+        },
+        messages: [{ role: 'user', content: 'hello' }],
+      },
+      surface: 'openai-chat',
+    });
+
+    expect(request).toMatchObject({
+      requestedModel: 'gpt-5',
+      stream: true,
+      metadata: { user_id: 'user-1' },
+      tools: [{
+        name: 'Glob',
+        description: 'Search files',
+        strict: true,
+        inputSchema: {
+          type: 'object',
+          properties: {
+            pattern: { type: 'string' },
+          },
+        },
+      }],
+      toolChoice: {
+        type: 'tool',
+        name: 'Glob',
+      },
+    });
+  });
+
+  it('parses anthropic-shaped tools from compatibility bodies', () => {
+    const request = canonicalRequestFromOpenAiBody({
+      body: {
+        model: 'gpt-5',
+        tools: [{
+          name: 'Glob',
+          description: 'Search files',
+          input_schema: {
+            type: 'object',
+            properties: {
+              pattern: { type: 'string' },
+            },
+          },
+        }],
+        tool_choice: {
+          type: 'tool',
+          name: 'Glob',
+        },
+        messages: [{ role: 'user', content: 'hello' }],
+      },
+      surface: 'openai-chat',
+    });
+
+    expect(request.tools).toEqual([{
+      name: 'Glob',
+      description: 'Search files',
+      inputSchema: {
+        type: 'object',
+        properties: {
+          pattern: { type: 'string' },
+        },
+      },
+    }]);
+    expect(request.toolChoice).toEqual({
+      type: 'tool',
+      name: 'Glob',
+    });
+  });
+
+  it('builds metadata back into OpenAI chat requests', () => {
+    const body = canonicalRequestToOpenAiChatBody({
+      operation: 'generate',
+      surface: 'openai-chat',
+      cliProfile: 'generic',
+      requestedModel: 'gpt-5',
+      stream: false,
+      messages: [{ role: 'user', parts: [{ type: 'text', text: 'hello' }] }],
+      metadata: { user_id: 'user-1' },
+      toolChoice: {
+        type: 'tool',
+        name: 'Glob',
+      },
+      tools: [{
+        name: 'Glob',
+        strict: true,
+        inputSchema: {
+          type: 'object',
+          properties: {
+            pattern: { type: 'string' },
+          },
+        },
+      }],
+    });
+
+    expect(body).toMatchObject({
+      model: 'gpt-5',
+      metadata: { user_id: 'user-1' },
+      tool_choice: {
+        type: 'function',
+        function: {
+          name: 'Glob',
+        },
+      },
+      tools: [{
+        type: 'function',
+        function: {
+          name: 'Glob',
+          strict: true,
+          parameters: {
+            type: 'object',
+            properties: {
+              pattern: { type: 'string' },
+            },
+          },
+        },
+      }],
+    });
+  });
+
+  it('round-trips include continuity metadata back into OpenAI-compatible bodies', () => {
+    const request = canonicalRequestFromOpenAiBody({
+      body: {
+        model: 'gpt-5',
+        stream: true,
+        include: ['reasoning.encrypted_content', 'message.input_image.image_url'],
+        reasoning: {
+          effort: 'high',
+        },
+        messages: [{ role: 'user', content: 'hello' }],
+      },
+      surface: 'openai-responses',
+    });
+
+    const body = canonicalRequestToOpenAiChatBody(request);
+
+    expect(body).toMatchObject({
+      model: 'gpt-5',
+      reasoning_effort: 'high',
+      include: ['reasoning.encrypted_content', 'message.input_image.image_url'],
+    });
+  });
 });
diff --git a/src/server/transformers/canonical/request.ts b/src/server/transformers/canonical/request.ts
index 74d58a1..92aec80 100644
--- a/src/server/transformers/canonical/request.ts
+++ b/src/server/transformers/canonical/request.ts
@@ -197,6 +197,13 @@ function parseToolChoice(rawToolChoice: unknown): CanonicalToolChoice | undefine
   const type = asTrimmedString(rawToolChoice.type).toLowerCase();
   if (type === 'auto' || type === 'none') return type;
   if (type === 'any' || type === 'required') return 'required';
+  if (type === 'function') {
+    const name = asTrimmedString(
+      (isRecord(rawToolChoice.function) ? rawToolChoice.function.name : undefined)
+      ?? rawToolChoice.name,
+    );
+    return name ? { type: 'tool', name } : undefined;
+  }
   if (type !== 'tool') return undefined;
 
   const name = asTrimmedString(
@@ -212,8 +219,9 @@ function parseTools(rawTools: unknown): CanonicalTool[] | undefined {
   const tools = rawTools
     .flatMap((item) => {
       if (!isRecord(item)) return [];
+      const itemType = asTrimmedString(item.type).toLowerCase();
 
-      if (asTrimmedString(item.type).toLowerCase() === 'function' && isRecord(item.function)) {
+      if (itemType === 'function' && isRecord(item.function)) {
         const name = asTrimmedString(item.function.name);
         if (!name) return [];
         return [{
@@ -221,10 +229,24 @@ function parseTools(rawTools: unknown): CanonicalTool[] | undefined {
           ...(asTrimmedString(item.function.description)
             ? { description: asTrimmedString(item.function.description) }
             : {}),
+          ...(typeof item.function.strict === 'boolean' ? { strict: item.function.strict } : {}),
           ...(isRecord(item.function.parameters) ? { inputSchema: cloneJsonValue(item.function.parameters) } : {}),
         }];
       }
 
+      if ((itemType === '' || itemType === 'tool') && asTrimmedString(item.name)) {
+        return [{
+          name: asTrimmedString(item.name),
+          ...(asTrimmedString(item.description)
+            ? { description: asTrimmedString(item.description) }
+            : {}),
+          ...(typeof item.strict === 'boolean' ? { strict: item.strict } : {}),
+          ...(isRecord(item.input_schema)
+            ? { inputSchema: cloneJsonValue(item.input_schema) }
+            : (isRecord(item.inputSchema) ? { inputSchema: cloneJsonValue(item.inputSchema) } : {})),
+        }];
+      }
+
       if (Array.isArray(item.functionDeclarations)) {
         return item.functionDeclarations.flatMap((declaration) => {
           if (!isRecord(declaration)) return [];
@@ -252,6 +274,9 @@ export function canonicalRequestFromOpenAiBody(
   input: CanonicalRequestFromOpenAiBodyInput,
 ): CanonicalRequestEnvelope {
   const body = input.body;
+  const metadata = isRecord(input.metadata)
+    ? input.metadata
+    : (isRecord(body.metadata) ? cloneJsonValue(body.metadata) : undefined);
   const messages: CanonicalMessage[] = [];
   const rawMessages = Array.isArray(body.messages) ? body.messages : [];
 
@@ -329,7 +354,7 @@ export function canonicalRequestFromOpenAiBody(
     ...(parseTools(body.tools) ? { tools: parseTools(body.tools) } : {}),
     ...(parseToolChoice(body.tool_choice) !== undefined ? { toolChoice: parseToolChoice(body.tool_choice) } : {}),
     ...(Object.keys(continuation).length > 0 ? { continuation } : {}),
-    ...(input.metadata ? { metadata: input.metadata } : {}),
+    ...(metadata ? { metadata } : {}),
     ...((reasoningResult.metadata || input.passthrough)
       ? {
         passthrough: {
@@ -478,6 +503,20 @@ export function canonicalRequestToOpenAiChatBody(
   if (request.reasoning?.effort) body.reasoning_effort = request.reasoning.effort;
   if (request.reasoning?.budgetTokens !== undefined) body.reasoning_budget = request.reasoning.budgetTokens;
   if (request.reasoning?.summary) body.reasoning_summary = request.reasoning.summary;
+  const transformerMetadata = isRecord(request.passthrough?.transformerMetadata)
+    ? request.passthrough.transformerMetadata as Record<string, unknown>
+    : null;
+  const passthroughInclude = Array.isArray(transformerMetadata?.include)
+    ? (transformerMetadata.include as unknown[])
+      .filter((item): item is string => typeof item === 'string' && item.trim().length > 0)
+      .map((item) => item.trim())
+    : [];
+  const mergedInclude = [
+    ...(request.reasoning?.includeEncryptedContent ? ['reasoning.encrypted_content'] : []),
+    ...passthroughInclude,
+  ].filter((item, index, all) => all.indexOf(item) === index);
+  if (mergedInclude.length > 0) body.include = mergedInclude;
+  if (request.metadata !== undefined) body.metadata = cloneJsonValue(request.metadata);
   if (request.continuation?.promptCacheKey) body.prompt_cache_key = request.continuation.promptCacheKey;
   if (request.continuation?.previousResponseId) body.previous_response_id = request.continuation.previousResponseId;
   if (Array.isArray(request.tools) && request.tools.length > 0) {
@@ -486,6 +525,7 @@ export function canonicalRequestToOpenAiChatBody(
       function: {
         name: tool.name,
         ...(tool.description ? { description: tool.description } : {}),
+        ...(typeof tool.strict === 'boolean' ? { strict: tool.strict } : {}),
         parameters: cloneJsonValue(tool.inputSchema ?? { type: 'object' }),
       },
     }));
diff --git a/src/server/transformers/canonical/tools.ts b/src/server/transformers/canonical/tools.ts
index 55b0be4..9600d18 100644
--- a/src/server/transformers/canonical/tools.ts
+++ b/src/server/transformers/canonical/tools.ts
@@ -1,6 +1,7 @@
 export type CanonicalTool = {
   name: string;
   description?: string;
+  strict?: boolean;
   inputSchema?: Record<string, unknown> | null;
 };
 
diff --git a/src/server/transformers/openai/responses/aggregator.test.ts b/src/server/transformers/openai/responses/aggregator.test.ts
index 36266ed..17d0765 100644
--- a/src/server/transformers/openai/responses/aggregator.test.ts
+++ b/src/server/transformers/openai/responses/aggregator.test.ts
@@ -389,6 +389,54 @@ describe('serializeConvertedResponsesEvents', () => {
     });
   });
 
+  it('emits terminal done events before relaying an upstream response.completed event', () => {
+    const state = createOpenAiResponsesAggregateState('gpt-5');
+    const streamContext = createStreamTransformContext('gpt-5');
+    const usage = {
+      promptTokens: 2,
+      completionTokens: 4,
+      totalTokens: 6,
+    };
+
+    serializeConvertedResponsesEvents({
+      state,
+      streamContext,
+      usage,
+      event: {
+        contentDelta: 'hello world',
+      } as any,
+    });
+
+    const completionLines = serializeConvertedResponsesEvents({
+      state,
+      streamContext,
+      usage,
+      event: {
+        responsesEventType: 'response.completed',
+        responsesPayload: {
+          type: 'response.completed',
+          response: {
+            id: 'resp_done_1',
+            model: 'gpt-5',
+            usage: {
+              input_tokens: 2,
+              output_tokens: 4,
+              total_tokens: 6,
+            },
+          },
+        },
+      },
+    });
+
+    const events = parseSseEvents(completionLines);
+    expect(events.map((entry) => entry.event ?? 'data')).toEqual([
+      'response.output_text.done',
+      'response.content_part.done',
+      'response.output_item.done',
+      'response.completed',
+    ]);
+  });
+
   it('emits canonical reasoning done events before response.completed when recovering sparse reasoning output', () => {
     const state = createOpenAiResponsesAggregateState('gpt-5');
     const streamContext = createStreamTransformContext('gpt-5');
@@ -763,4 +811,433 @@ describe('serializeConvertedResponsesEvents', () => {
       },
     });
   });
+
+  it('emits terminal done events before forwarding an upstream response.completed event', () => {
+    const state = createOpenAiResponsesAggregateState('gpt-5');
+    const streamContext = createStreamTransformContext('gpt-5');
+    const usage = {
+      promptTokens: 2,
+      completionTokens: 4,
+      totalTokens: 6,
+    };
+
+    serializeConvertedResponsesEvents({
+      state,
+      streamContext,
+      usage,
+      event: {
+        contentDelta: 'hello world',
+      } as any,
+    });
+
+    const lines = serializeConvertedResponsesEvents({
+      state,
+      streamContext,
+      usage,
+      event: {
+        responsesEventType: 'response.completed',
+        responsesPayload: {
+          type: 'response.completed',
+          response: {
+            id: 'resp_1',
+            model: 'gpt-5',
+            usage: {
+              input_tokens: 2,
+              output_tokens: 4,
+              total_tokens: 6,
+            },
+          },
+        },
+      },
+    });
+
+    const events = parseSseEvents(lines);
+    expect(events.map((entry) => entry.event)).toEqual([
+      'response.output_text.done',
+      'response.content_part.done',
+      'response.output_item.done',
+      'response.completed',
+    ]);
+  });
+
+  it('closes reasoning summary parts before forwarding an upstream response.completed event', () => {
+    const state = createOpenAiResponsesAggregateState('gpt-5');
+    const streamContext = createStreamTransformContext('gpt-5');
+    const usage = {
+      promptTokens: 1,
+      completionTokens: 2,
+      totalTokens: 3,
+    };
+
+    serializeConvertedResponsesEvents({
+      state,
+      streamContext,
+      usage,
+      event: {
+        reasoningDelta: 'Think ',
+      } as any,
+    });
+
+    const lines = serializeConvertedResponsesEvents({
+      state,
+      streamContext,
+      usage,
+      event: {
+        responsesEventType: 'response.completed',
+        responsesPayload: {
+          type: 'response.completed',
+          response: {
+            id: 'resp_reasoning_done',
+            model: 'gpt-5',
+            usage: {
+              input_tokens: 1,
+              output_tokens: 2,
+              total_tokens: 3,
+            },
+          },
+        },
+      },
+    });
+
+    const events = parseSseEvents(lines);
+    expect(events.map((entry) => entry.event)).toEqual([
+      'response.reasoning_summary_text.done',
+      'response.reasoning_summary_part.done',
+      'response.output_item.done',
+      'response.completed',
+    ]);
+  });
+
+  it('preserves response.incomplete as a first-class terminal event', () => {
+    const state = createOpenAiResponsesAggregateState('gpt-5');
+    const streamContext = createStreamTransformContext('gpt-5');
+    const usage = {
+      promptTokens: 2,
+      completionTokens: 4,
+      totalTokens: 6,
+    };
+
+    serializeConvertedResponsesEvents({
+      state,
+      streamContext,
+      usage,
+      event: {
+        contentDelta: 'partial answer',
+      } as any,
+    });
+
+    const lines = serializeConvertedResponsesEvents({
+      state,
+      streamContext,
+      usage,
+      event: {
+        responsesEventType: 'response.incomplete',
+        responsesPayload: {
+          type: 'response.incomplete',
+          response: {
+            id: 'resp_incomplete_1',
+            model: 'gpt-5',
+            status: 'incomplete',
+            incomplete_details: {
+              reason: 'max_output_tokens',
+            },
+            usage: {
+              input_tokens: 2,
+              output_tokens: 4,
+              total_tokens: 6,
+            },
+          },
+        },
+      },
+    });
+
+    const events = parseSseEvents(lines);
+    expect(events.map((entry) => entry.event)).toEqual([
+      'response.output_text.done',
+      'response.content_part.done',
+      'response.output_item.done',
+      'response.incomplete',
+    ]);
+    expect(events[3]?.payload).toMatchObject({
+      type: 'response.incomplete',
+      response: {
+        id: 'resp_incomplete_1',
+        status: 'incomplete',
+        incomplete_details: {
+          reason: 'max_output_tokens',
+        },
+        output_text: 'partial answer',
+      },
+    });
+  });
+
+  it('closes every unterminated message part and only emits output_text.done for text parts', () => {
+    const state = createOpenAiResponsesAggregateState('gpt-5');
+    const streamContext = createStreamTransformContext('gpt-5');
+    const usage = {
+      promptTokens: 1,
+      completionTokens: 2,
+      totalTokens: 3,
+    };
+
+    serializeConvertedResponsesEvents({
+      state,
+      streamContext,
+      usage,
+      event: {
+        responsesEventType: 'response.output_item.added',
+        responsesPayload: {
+          type: 'response.output_item.added',
+          output_index: 0,
+          item: {
+            id: 'msg_multi_1',
+            type: 'message',
+            role: 'assistant',
+            status: 'in_progress',
+            content: [],
+          },
+        },
+      },
+    });
+
+    serializeConvertedResponsesEvents({
+      state,
+      streamContext,
+      usage,
+      event: {
+        responsesEventType: 'response.content_part.added',
+        responsesPayload: {
+          type: 'response.content_part.added',
+          output_index: 0,
+          item_id: 'msg_multi_1',
+          content_index: 0,
+          part: {
+            type: 'refusal',
+            text: 'no',
+          },
+        },
+      },
+    });
+
+    serializeConvertedResponsesEvents({
+      state,
+      streamContext,
+      usage,
+      event: {
+        responsesEventType: 'response.content_part.added',
+        responsesPayload: {
+          type: 'response.content_part.added',
+          output_index: 0,
+          item_id: 'msg_multi_1',
+          content_index: 1,
+          part: {
+            type: 'output_text',
+            text: 'yes',
+          },
+        },
+      },
+    });
+
+    const lines = completeResponsesStream(state, streamContext, usage);
+    const events = parseSseEvents(lines);
+
+    expect(events.map((entry) => entry.event ?? (entry.payload === '[DONE]' ? '[DONE]' : 'data'))).toEqual([
+      'response.content_part.done',
+      'response.output_text.done',
+      'response.content_part.done',
+      'response.output_item.done',
+      'response.completed',
+      '[DONE]',
+    ]);
+    expect(events[0]?.payload).toMatchObject({
+      type: 'response.content_part.done',
+      content_index: 0,
+      part: {
+        type: 'refusal',
+        text: 'no',
+      },
+    });
+    expect(events[1]?.payload).toMatchObject({
+      type: 'response.output_text.done',
+      item_id: 'msg_multi_1',
+      text: 'yes',
+    });
+    expect(events[2]?.payload).toMatchObject({
+      type: 'response.content_part.done',
+      content_index: 1,
+      part: {
+        type: 'output_text',
+        text: 'yes',
+      },
+    });
+  });
+
+  it('closes every unterminated reasoning summary part before completion', () => {
+    const state = createOpenAiResponsesAggregateState('gpt-5');
+    const streamContext = createStreamTransformContext('gpt-5');
+    const usage = {
+      promptTokens: 1,
+      completionTokens: 2,
+      totalTokens: 3,
+    };
+
+    serializeConvertedResponsesEvents({
+      state,
+      streamContext,
+      usage,
+      event: {
+        responsesEventType: 'response.output_item.added',
+        responsesPayload: {
+          type: 'response.output_item.added',
+          output_index: 0,
+          item: {
+            id: 'rs_multi_1',
+            type: 'reasoning',
+            status: 'in_progress',
+            summary: [],
+          },
+        },
+      },
+    });
+
+    for (const [summaryIndex, text] of [[0, 'first'], [1, 'second']] as const) {
+      serializeConvertedResponsesEvents({
+        state,
+        streamContext,
+        usage,
+        event: {
+          responsesEventType: 'response.reasoning_summary_part.added',
+          responsesPayload: {
+            type: 'response.reasoning_summary_part.added',
+            item_id: 'rs_multi_1',
+            output_index: 0,
+            summary_index: summaryIndex,
+            part: {
+              type: 'summary_text',
+              text,
+            },
+          },
+        },
+      });
+    }
+
+    const lines = completeResponsesStream(state, streamContext, usage);
+    const events = parseSseEvents(lines);
+
+    expect(events.map((entry) => entry.event ?? (entry.payload === '[DONE]' ? '[DONE]' : 'data'))).toEqual([
+      'response.reasoning_summary_text.done',
+      'response.reasoning_summary_part.done',
+      'response.reasoning_summary_text.done',
+      'response.reasoning_summary_part.done',
+      'response.output_item.done',
+      'response.completed',
+      '[DONE]',
+    ]);
+    expect(events[0]?.payload).toMatchObject({
+      type: 'response.reasoning_summary_text.done',
+      summary_index: 0,
+      text: 'first',
+    });
+    expect(events[2]?.payload).toMatchObject({
+      type: 'response.reasoning_summary_text.done',
+      summary_index: 1,
+      text: 'second',
+    });
+  });
+
+  it('does not synthesize duplicate tool input done events after original tool completion already arrived', () => {
+    const state = createOpenAiResponsesAggregateState('gpt-5');
+    const streamContext = createStreamTransformContext('gpt-5');
+    const usage = {
+      promptTokens: 1,
+      completionTokens: 2,
+      totalTokens: 3,
+    };
+
+    serializeConvertedResponsesEvents({
+      state,
+      streamContext,
+      usage,
+      event: {
+        responsesEventType: 'response.output_item.added',
+        responsesPayload: {
+          type: 'response.output_item.added',
+          output_index: 0,
+          item: {
+            id: 'fc_done_1',
+            type: 'function_call',
+            status: 'in_progress',
+            call_id: 'fc_done_1',
+            name: 'browser',
+            arguments: '',
+          },
+        },
+      },
+    });
+
+    serializeConvertedResponsesEvents({
+      state,
+      streamContext,
+      usage,
+      event: {
+        responsesEventType: 'response.function_call_arguments.done',
+        responsesPayload: {
+          type: 'response.function_call_arguments.done',
+          item_id: 'fc_done_1',
+          call_id: 'fc_done_1',
+          output_index: 0,
+          name: 'browser',
+          arguments: '{"url":"https://example.com"}',
+        },
+      },
+    });
+
+    serializeConvertedResponsesEvents({
+      state,
+      streamContext,
+      usage,
+      event: {
+        responsesEventType: 'response.output_item.added',
+        responsesPayload: {
+          type: 'response.output_item.added',
+          output_index: 1,
+          item: {
+            id: 'ct_done_1',
+            type: 'custom_tool_call',
+            status: 'in_progress',
+            call_id: 'ct_done_1',
+            name: 'browser',
+            input: '',
+          },
+        },
+      },
+    });
+
+    serializeConvertedResponsesEvents({
+      state,
+      streamContext,
+      usage,
+      event: {
+        responsesEventType: 'response.custom_tool_call_input.done',
+        responsesPayload: {
+          type: 'response.custom_tool_call_input.done',
+          item_id: 'ct_done_1',
+          call_id: 'ct_done_1',
+          output_index: 1,
+          name: 'browser',
+          input: 'open example.com',
+        },
+      },
+    });
+
+    const lines = completeResponsesStream(state, streamContext, usage);
+    const events = parseSseEvents(lines);
+
+    expect(events.map((entry) => entry.event ?? (entry.payload === '[DONE]' ? '[DONE]' : 'data'))).toEqual([
+      'response.output_item.done',
+      'response.output_item.done',
+      'response.completed',
+      '[DONE]',
+    ]);
+  });
 });
diff --git a/src/server/transformers/openai/responses/aggregator.ts b/src/server/transformers/openai/responses/aggregator.ts
index 701ad6b..fde6662 100644
--- a/src/server/transformers/openai/responses/aggregator.ts
+++ b/src/server/transformers/openai/responses/aggregator.ts
@@ -61,6 +61,8 @@ const outputTextDoneMarker = Symbol('responses.output_text.done');
 const contentPartDoneMarker = Symbol('responses.content_part.done');
 const reasoningSummaryTextDoneMarker = Symbol('responses.reasoning_summary_text.done');
 const reasoningSummaryPartDoneMarker = Symbol('responses.reasoning_summary_part.done');
+const functionCallArgumentsDoneMarker = Symbol('responses.function_call_arguments.done');
+const customToolInputDoneMarker = Symbol('responses.custom_tool_call_input.done');
 
 export type OpenAiResponsesAggregateState = {
   modelName: string;
@@ -76,6 +78,7 @@ export type OpenAiResponsesAggregateState = {
   usageExtras: Record<string, unknown>;
   completed: boolean;
   failed: boolean;
+  incomplete: boolean;
 };
 
 export function createOpenAiResponsesAggregateState(modelName: string): OpenAiResponsesAggregateState {
@@ -93,6 +96,7 @@ export function createOpenAiResponsesAggregateState(modelName: string): OpenAiRe
     usageExtras: {},
     completed: false,
     failed: false,
+    incomplete: false,
   };
 }
 
@@ -395,7 +399,7 @@ function materializeResponse(
   streamContext: StreamTransformContext,
   usage: ResponsesUsageSummary,
   responseTemplate?: Record<string, unknown> | null,
-  statusOverride?: 'completed' | 'failed',
+  statusOverride?: 'completed' | 'failed' | 'incomplete',
 ): Record<string, unknown> {
   const base = cloneRecord(responseTemplate) || {};
   const responseId = ensureResponseId(
@@ -417,7 +421,7 @@ function materializeResponse(
         ...item,
         status: status && status !== 'in_progress'
           ? status
-          : (state.failed ? 'failed' : 'completed'),
+          : (state.failed ? 'failed' : state.incomplete ? 'incomplete' : 'completed'),
       };
     });
 
@@ -426,7 +430,7 @@ function materializeResponse(
     id: responseId,
     object: 'response',
     created_at: createdAt,
-    status: statusOverride ?? (state.failed ? 'failed' : 'completed'),
+    status: statusOverride ?? (state.failed ? 'failed' : state.incomplete ? 'incomplete' : 'completed'),
     model: asTrimmedString(base.model) || streamContext.model || state.modelName,
     output,
     output_text: collectOutputText(state),
@@ -497,6 +501,9 @@ function applyOriginalResponsesPayload(
             ...reasoningState.item,
             ...item,
           };
+          if (eventType === 'response.output_item.done' && !asTrimmedString(next.status)) {
+            next.status = 'completed';
+          }
           if ((!Array.isArray(item.summary) || item.summary.length === 0) && Array.isArray(reasoningState.item.summary)) {
             next.summary = reasoningState.item.summary;
           }
@@ -512,6 +519,9 @@ function applyOriginalResponsesPayload(
           ...existing,
           ...item,
         };
+        if (eventType === 'response.output_item.done' && !asTrimmedString(next.status)) {
+          next.status = 'completed';
+        }
         if ((!Array.isArray(item.content) || item.content.length === 0) && Array.isArray(existing.content)) {
           next.content = existing.content;
         }
@@ -575,6 +585,7 @@ function applyOriginalResponsesPayload(
       );
       if (eventType === 'response.function_call_arguments.done') {
         entry.item.arguments = typeof payload.arguments === 'string' ? payload.arguments : String(payload.arguments ?? '');
+        markTerminalMarker(entry.item, functionCallArgumentsDoneMarker);
       } else {
         entry.item.arguments = `${typeof entry.item.arguments === 'string' ? entry.item.arguments : ''}${typeof payload.delta === 'string' ? payload.delta : ''}`;
       }
@@ -591,6 +602,7 @@ function applyOriginalResponsesPayload(
       );
       if (eventType === 'response.custom_tool_call_input.done') {
         entry.item.input = typeof payload.input === 'string' ? payload.input : String(payload.input ?? '');
+        markTerminalMarker(entry.item, customToolInputDoneMarker);
       } else {
         entry.item.input = `${typeof entry.item.input === 'string' ? entry.item.input : ''}${typeof payload.delta === 'string' ? payload.delta : ''}`;
       }
@@ -654,17 +666,36 @@ function applyOriginalResponsesPayload(
     }
     case 'response.completed': {
       mergeUsageExtras(state, payload.response && isRecord(payload.response) ? payload.response.usage : payload.usage);
+      const terminalLines = buildSyntheticTerminalItemDoneEvents(state, 'completed');
       state.completed = true;
       const responsePayload = cloneRecord(payload.response);
       const materialized = materializeResponse(state, streamContext, usage, responsePayload, 'completed');
-      return [serializeSse('response.completed', { ...payload, response: materialized })];
+      return [
+        ...terminalLines,
+        serializeSse('response.completed', { ...payload, response: materialized }),
+      ];
     }
     case 'response.failed': {
       mergeUsageExtras(state, payload.response && isRecord(payload.response) ? payload.response.usage : payload.usage);
+      const terminalLines = buildSyntheticTerminalItemDoneEvents(state, 'failed');
       state.failed = true;
       const responsePayload = cloneRecord(payload.response);
       const materialized = materializeResponse(state, streamContext, usage, responsePayload, 'failed');
-      return [serializeSse('response.failed', { ...payload, response: materialized })];
+      return [
+        ...terminalLines,
+        serializeSse('response.failed', { ...payload, response: materialized }),
+      ];
+    }
+    case 'response.incomplete': {
+      mergeUsageExtras(state, payload.response && isRecord(payload.response) ? payload.response.usage : payload.usage);
+      const terminalLines = buildSyntheticTerminalItemDoneEvents(state, 'incomplete');
+      state.incomplete = true;
+      const responsePayload = cloneRecord(payload.response);
+      const materialized = materializeResponse(state, streamContext, usage, responsePayload, 'incomplete');
+      return [
+        ...terminalLines,
+        serializeSse('response.incomplete', { ...payload, response: materialized }),
+      ];
     }
     default:
       mergeUsageExtras(state, payload.usage);
@@ -803,7 +834,7 @@ function buildSyntheticToolEvents(
 
 function buildSyntheticTerminalItemDoneEvents(
   state: OpenAiResponsesAggregateState,
-  status: 'completed' | 'failed',
+  status: 'completed' | 'failed' | 'incomplete',
 ): string[] {
   const lines: string[] = [];
 
@@ -812,7 +843,7 @@ function buildSyntheticTerminalItemDoneEvents(
     if (!isRecord(item)) continue;
 
     const currentStatus = asTrimmedString(item.status).toLowerCase();
-    if (currentStatus === 'completed' || currentStatus === 'failed') continue;
+    if (currentStatus === 'completed' || currentStatus === 'failed' || currentStatus === 'incomplete') continue;
 
     const itemType = asTrimmedString(item.type).toLowerCase();
     const itemId = ensureOutputItemId(asTrimmedString(item.id), 'out', index);
@@ -820,10 +851,12 @@ function buildSyntheticTerminalItemDoneEvents(
 
     if (itemType === 'message') {
       const content = Array.isArray(item.content) ? item.content as AggregateOutputItem[] : [];
-      const part = content[0];
-      if (isRecord(part)) {
+      for (let contentIndex = 0; contentIndex < content.length; contentIndex += 1) {
+        const part = content[contentIndex];
+        if (!isRecord(part)) continue;
+        const partType = asTrimmedString(part.type).toLowerCase();
         const text = typeof part.text === 'string' ? part.text : String(part.text ?? '');
-        if (!hasTerminalMarker(part, outputTextDoneMarker)) {
+        if ((partType === 'output_text' || partType === 'text') && !hasTerminalMarker(part, outputTextDoneMarker)) {
           lines.push(serializeSse('response.output_text.done', {
             type: 'response.output_text.done',
             output_index: index,
@@ -837,7 +870,7 @@ function buildSyntheticTerminalItemDoneEvents(
             type: 'response.content_part.done',
             output_index: index,
             item_id: itemId,
-            content_index: 0,
+            content_index: contentIndex,
             part: cloneJson(part),
           }));
           markTerminalMarker(part, contentPartDoneMarker);
@@ -845,15 +878,16 @@ function buildSyntheticTerminalItemDoneEvents(
       }
     } else if (itemType === 'reasoning') {
       const summary = Array.isArray(item.summary) ? item.summary as AggregateOutputItem[] : [];
-      const part = summary[0];
-      if (isRecord(part)) {
+      for (let summaryIndex = 0; summaryIndex < summary.length; summaryIndex += 1) {
+        const part = summary[summaryIndex];
+        if (!isRecord(part)) continue;
         const text = typeof part.text === 'string' ? part.text : String(part.text ?? '');
         if (!hasTerminalMarker(part, reasoningSummaryTextDoneMarker)) {
           lines.push(serializeSse('response.reasoning_summary_text.done', {
             type: 'response.reasoning_summary_text.done',
             item_id: itemId,
             output_index: index,
-            summary_index: 0,
+            summary_index: summaryIndex,
             text,
           }));
           markTerminalMarker(part, reasoningSummaryTextDoneMarker);
@@ -863,7 +897,7 @@ function buildSyntheticTerminalItemDoneEvents(
             type: 'response.reasoning_summary_part.done',
             item_id: itemId,
             output_index: index,
-            summary_index: 0,
+            summary_index: summaryIndex,
             part: cloneJson(part),
           }));
           markTerminalMarker(part, reasoningSummaryPartDoneMarker);
@@ -873,26 +907,32 @@ function buildSyntheticTerminalItemDoneEvents(
       const callId = asTrimmedString(item.call_id) || itemId;
       const name = asTrimmedString(item.name);
       const argumentsText = typeof item.arguments === 'string' ? item.arguments : String(item.arguments ?? '');
-      lines.push(serializeSse('response.function_call_arguments.done', {
-        type: 'response.function_call_arguments.done',
-        item_id: itemId,
-        call_id: callId,
-        output_index: index,
-        ...(name ? { name } : {}),
-        arguments: argumentsText,
-      }));
+      if (!hasTerminalMarker(item, functionCallArgumentsDoneMarker)) {
+        lines.push(serializeSse('response.function_call_arguments.done', {
+          type: 'response.function_call_arguments.done',
+          item_id: itemId,
+          call_id: callId,
+          output_index: index,
+          ...(name ? { name } : {}),
+          arguments: argumentsText,
+        }));
+        markTerminalMarker(item, functionCallArgumentsDoneMarker);
+      }
     } else if (itemType === 'custom_tool_call') {
       const callId = asTrimmedString(item.call_id) || itemId;
       const name = asTrimmedString(item.name);
       const inputText = typeof item.input === 'string' ? item.input : String(item.input ?? '');
-      lines.push(serializeSse('response.custom_tool_call_input.done', {
-        type: 'response.custom_tool_call_input.done',
-        item_id: itemId,
-        call_id: callId,
-        output_index: index,
-        ...(name ? { name } : {}),
-        input: inputText,
-      }));
+      if (!hasTerminalMarker(item, customToolInputDoneMarker)) {
+        lines.push(serializeSse('response.custom_tool_call_input.done', {
+          type: 'response.custom_tool_call_input.done',
+          item_id: itemId,
+          call_id: callId,
+          output_index: index,
+          ...(name ? { name } : {}),
+          input: inputText,
+        }));
+        markTerminalMarker(item, customToolInputDoneMarker);
+      }
     }
 
     item.status = status;
@@ -941,7 +981,7 @@ export function completeResponsesStream(
   streamContext: StreamTransformContext,
   usage: ResponsesUsageSummary,
 ): string[] {
-  if (state.failed || state.completed) {
+  if (state.failed || state.completed || state.incomplete) {
     return [serializeDone()];
   }
   const lines = buildSyntheticTerminalItemDoneEvents(state, 'completed');
@@ -986,3 +1026,25 @@ export function failResponsesStream(
     serializeDone(),
   ];
 }
+
+export function incompleteResponsesStream(
+  state: OpenAiResponsesAggregateState,
+  streamContext: StreamTransformContext,
+  usage: ResponsesUsageSummary,
+  payload: unknown,
+): string[] {
+  if (state.failed || state.completed || state.incomplete) {
+    return [serializeDone()];
+  }
+  const lines = buildSyntheticTerminalItemDoneEvents(state, 'incomplete');
+  state.incomplete = true;
+  const incompletePayload = cloneRecord(payload);
+  return [
+    ...lines,
+    serializeSse('response.incomplete', {
+      ...incompletePayload,
+      response: materializeResponse(state, streamContext, usage, cloneRecord(incompletePayload?.response), 'incomplete'),
+    }),
+    serializeDone(),
+  ];
+}
diff --git a/src/server/transformers/openai/responses/compatibility.ts b/src/server/transformers/openai/responses/compatibility.ts
index fe9be9a..960a8a5 100644
--- a/src/server/transformers/openai/responses/compatibility.ts
+++ b/src/server/transformers/openai/responses/compatibility.ts
@@ -61,6 +61,8 @@ export function buildResponsesCompatibilityBodies(
     if (instructions !== null) richCandidate.instructions = instructions;
 
     const passthroughFields = [
+      'tools',
+      'tool_choice',
       'parallel_tool_calls',
       'include',
       'reasoning',
@@ -228,6 +230,8 @@ function buildStrictResponsesBody(
     model,
     input: body.input,
     stream: body.stream === true,
+    ...(body.tools !== undefined ? { tools: cloneJsonValue(body.tools) } : {}),
+    ...(body.tool_choice !== undefined ? { tool_choice: cloneJsonValue(body.tool_choice) } : {}),
     ...(explicitInstructions !== null
       ? { instructions: explicitInstructions }
       : {}),
diff --git a/src/server/transformers/openai/responses/conversion.test.ts b/src/server/transformers/openai/responses/conversion.test.ts
index c54b3db..c146ad5 100644
--- a/src/server/transformers/openai/responses/conversion.test.ts
+++ b/src/server/transformers/openai/responses/conversion.test.ts
@@ -1109,6 +1109,219 @@ describe('convertResponsesBodyToOpenAiBody', () => {
     });
   });
 
+  it('preserves tools and tool_choice across all compatibility retry bodies', () => {
+    const candidates = buildResponsesCompatibilityBodies({
+      model: 'gpt-5',
+      input: 'hello',
+      stream: true,
+      metadata: { user_id: 'user-1' },
+      instructions: 'be helpful',
+      tools: [{
+        type: 'function',
+        function: {
+          name: 'lookup_weather',
+          parameters: {
+            type: 'object',
+            properties: {
+              city: { type: 'string' },
+            },
+          },
+        },
+      }],
+      tool_choice: {
+        type: 'function',
+        function: {
+          name: 'lookup_weather',
+        },
+      },
+    });
+
+    expect(candidates.length).toBeGreaterThan(0);
+    for (const candidate of candidates) {
+      expect(candidate.tools).toEqual([{
+        type: 'function',
+        function: {
+          name: 'lookup_weather',
+          parameters: {
+            type: 'object',
+            properties: {
+              city: { type: 'string' },
+            },
+          },
+        },
+      }]);
+      expect(candidate.tool_choice).toEqual({
+        type: 'function',
+        function: {
+          name: 'lookup_weather',
+        },
+      });
+    }
+  });
+
+  it('maps native tool choices and strict function tools into OpenAI-compatible fallback bodies', () => {
+    const result = convertResponsesBodyToOpenAiBody(
+      {
+        model: 'gpt-5',
+        input: 'hello',
+        tools: [{
+          type: 'function',
+          name: 'lookup_weather',
+          parameters: {
+            type: 'object',
+            properties: {
+              city: { type: 'string' },
+            },
+          },
+          strict: true,
+        }],
+        tool_choice: {
+          type: 'tool',
+          name: 'lookup_weather',
+        },
+      },
+      'gpt-5',
+      false,
+    );
+
+    expect(result.tools).toEqual([{
+      type: 'function',
+      function: {
+        name: 'lookup_weather',
+        parameters: {
+          type: 'object',
+          properties: {
+            city: { type: 'string' },
+          },
+        },
+        strict: true,
+      },
+    }]);
+    expect(result.tool_choice).toEqual({
+      type: 'function',
+      function: {
+        name: 'lookup_weather',
+      },
+    });
+  });
+
+  it('derives Responses reasoning config from chat-style reasoning request fields', () => {
+    const result = convertOpenAiBodyToResponsesBody(
+      {
+        model: 'gpt-5',
+        messages: [{ role: 'user', content: 'hello' }],
+        reasoning_effort: 'high',
+        reasoning_budget: 2048,
+        reasoning_summary: 'detailed',
+      },
+      'gpt-5',
+      false,
+    );
+
+    expect(result).toMatchObject({
+      model: 'gpt-5',
+      reasoning: {
+        effort: 'high',
+        budget_tokens: 2048,
+        summary: 'detailed',
+      },
+    });
+  });
+
+  it('preserves assistant reasoning history when converting OpenAI-compatible bodies to Responses input', () => {
+    const result = convertOpenAiBodyToResponsesBody(
+      {
+        model: 'gpt-5',
+        messages: [{
+          role: 'assistant',
+          content: '',
+          reasoning_content: 'plan quietly',
+          reasoning_signature: 'sig_1',
+          tool_calls: [{
+            id: 'call_1',
+            type: 'function',
+            function: {
+              name: 'Glob',
+              arguments: '{"pattern":"README*"}',
+            },
+          }],
+        }],
+      },
+      'gpt-5',
+      false,
+    );
+
+    expect(result.input).toEqual([
+      {
+        type: 'reasoning',
+        summary: [{
+          type: 'summary_text',
+          text: 'plan quietly',
+        }],
+        encrypted_content: 'sig_1',
+      },
+      {
+        type: 'function_call',
+        call_id: 'call_1',
+        name: 'Glob',
+        arguments: '{"pattern":"README*"}',
+      },
+    ]);
+  });
+
+  it('preserves chat-native modalities and audio settings when converting to Responses bodies', () => {
+    const result = convertOpenAiBodyToResponsesBody(
+      {
+        model: 'gpt-5',
+        messages: [{ role: 'user', content: 'hello' }],
+        metadata: { user_id: 'user-1' },
+        modalities: ['text', 'audio'],
+        audio: {
+          voice: 'alloy',
+          format: 'mp3',
+        },
+      },
+      'gpt-5',
+      false,
+    );
+
+    expect(result).toMatchObject({
+      metadata: { user_id: 'user-1' },
+      modalities: ['text', 'audio'],
+      audio: {
+        voice: 'alloy',
+        format: 'mp3',
+      },
+    });
+  });
+
+  it('preserves metadata, modalities, and audio when converting Responses bodies back to OpenAI-compatible bodies', () => {
+    const result = convertResponsesBodyToOpenAiBody(
+      {
+        model: 'gpt-5',
+        input: 'hello',
+        metadata: { user_id: 'user-1' },
+        modalities: ['text', 'audio'],
+        audio: {
+          voice: 'alloy',
+          format: 'mp3',
+        },
+      },
+      'gpt-5',
+      false,
+    );
+
+    expect(result).toMatchObject({
+      model: 'gpt-5',
+      metadata: { user_id: 'user-1' },
+      modalities: ['text', 'audio'],
+      audio: {
+        voice: 'alloy',
+        format: 'mp3',
+      },
+    });
+  });
+
   it('maps Responses text.format back into OpenAI response_format', () => {
     const result = convertResponsesBodyToOpenAiBody(
       {
@@ -1151,6 +1364,27 @@ describe('convertResponsesBodyToOpenAiBody', () => {
     });
   });
 
+  it('preserves responses metadata when converting back to OpenAI-compatible bodies', () => {
+    const result = convertResponsesBodyToOpenAiBody(
+      {
+        model: 'gpt-5',
+        input: 'hello',
+        metadata: {
+          user_id: 'user-1',
+        },
+      },
+      'gpt-5',
+      false,
+    );
+
+    expect(result).toMatchObject({
+      model: 'gpt-5',
+      metadata: {
+        user_id: 'user-1',
+      },
+    });
+  });
+
   it('normalizes field parity when converting Responses input back to OpenAI-compatible input', () => {
     const result = convertResponsesBodyToOpenAiBody(
       {
diff --git a/src/server/transformers/openai/responses/conversion.ts b/src/server/transformers/openai/responses/conversion.ts
index 90ba91c..ed16d4d 100644
--- a/src/server/transformers/openai/responses/conversion.ts
+++ b/src/server/transformers/openai/responses/conversion.ts
@@ -179,6 +179,20 @@ function normalizeResponsesRequestFieldParity(
     normalized.text = textConfig;
   }
 
+  if (!isRecord(normalized.reasoning)) {
+    const reasoning: Record<string, unknown> = {};
+    const effort = normalizeOptionalTrimmedString((normalized as Record<string, unknown>).reasoning_effort);
+    if (effort) reasoning.effort = effort;
+    const budgetTokens = toFiniteIntegerLike((normalized as Record<string, unknown>).reasoning_budget);
+    if (budgetTokens !== null) reasoning.budget_tokens = budgetTokens;
+    const summary = normalizeOptionalTrimmedString((normalized as Record<string, unknown>).reasoning_summary);
+    if (summary) reasoning.summary = summary;
+    if (Object.keys(reasoning).length > 0) normalized.reasoning = reasoning;
+  }
+  delete normalized.reasoning_effort;
+  delete normalized.reasoning_budget;
+  delete normalized.reasoning_summary;
+
   return normalized;
 }
 
@@ -448,6 +462,28 @@ export function convertOpenAiBodyToResponsesBody(
     }
 
     if (role === 'assistant') {
+      const reasoningContent = extractTextContent(
+        item.reasoning_content
+        ?? item.reasoning
+        ?? item.thinking,
+      ).trim();
+      const reasoningSignature = asTrimmedString(item.reasoning_signature);
+      if (reasoningContent || reasoningSignature) {
+        const reasoningItem: Record<string, unknown> = {
+          type: 'reasoning',
+        };
+        if (reasoningContent) {
+          reasoningItem.summary = [{
+            type: 'summary_text',
+            text: reasoningContent,
+          }];
+        }
+        if (reasoningSignature) {
+          reasoningItem.encrypted_content = reasoningSignature;
+        }
+        inputItems.push(reasoningItem);
+      }
+
       const normalizedContent = normalizeResponsesMessageContent('assistant', item.content);
       if (normalizedContent.length > 0) {
         inputItems.push({
@@ -527,7 +563,12 @@ export function convertOpenAiBodyToResponsesBody(
   if (topP !== null) body.top_p = topP;
 
   if (openaiBody.metadata !== undefined) body.metadata = openaiBody.metadata;
+  if (openaiBody.modalities !== undefined) body.modalities = cloneJsonValue(openaiBody.modalities);
+  if (openaiBody.audio !== undefined) body.audio = cloneJsonValue(openaiBody.audio);
   if (openaiBody.reasoning !== undefined) body.reasoning = openaiBody.reasoning;
+  if (openaiBody.reasoning_effort !== undefined) body.reasoning_effort = openaiBody.reasoning_effort;
+  if (openaiBody.reasoning_budget !== undefined) body.reasoning_budget = openaiBody.reasoning_budget;
+  if (openaiBody.reasoning_summary !== undefined) body.reasoning_summary = openaiBody.reasoning_summary;
   if (openaiBody.parallel_tool_calls !== undefined) body.parallel_tool_calls = openaiBody.parallel_tool_calls;
   if (openaiBody.tools !== undefined) body.tools = convertOpenAiToolsToResponses(openaiBody.tools, toolNameMap);
   if (openaiBody.safety_identifier !== undefined) body.safety_identifier = openaiBody.safety_identifier;
@@ -696,6 +737,14 @@ function convertResponsesToolChoiceToOpenAi(rawToolChoice: unknown): unknown {
   if (!isRecord(rawToolChoice)) return rawToolChoice;
 
   const type = asTrimmedString(rawToolChoice.type).toLowerCase();
+  if (type === 'tool') {
+    const name = asTrimmedString(rawToolChoice.name);
+    if (!name) return 'required';
+    return {
+      type: 'function',
+      function: { name },
+    };
+  }
   if (type === 'function') {
     if (isRecord(rawToolChoice.function) && asTrimmedString(rawToolChoice.function.name)) {
       return rawToolChoice;
@@ -845,6 +894,9 @@ export function convertResponsesBodyToOpenAiBody(
   if (typeof normalizedBody.max_output_tokens === 'number' && Number.isFinite(normalizedBody.max_output_tokens)) {
     payload.max_tokens = normalizedBody.max_output_tokens;
   }
+  if (normalizedBody.metadata !== undefined) payload.metadata = cloneJsonValue(normalizedBody.metadata);
+  if (normalizedBody.modalities !== undefined) payload.modalities = cloneJsonValue(normalizedBody.modalities);
+  if (normalizedBody.audio !== undefined) payload.audio = cloneJsonValue(normalizedBody.audio);
   if (normalizedBody.parallel_tool_calls !== undefined) payload.parallel_tool_calls = normalizedBody.parallel_tool_calls;
   if (normalizedBody.tools !== undefined) payload.tools = convertResponsesToolsToOpenAi(normalizedBody.tools);
   if (normalizedBody.tool_choice !== undefined) payload.tool_choice = convertResponsesToolChoiceToOpenAi(normalizedBody.tool_choice);
diff --git a/src/server/transformers/openai/responses/outbound.test.ts b/src/server/transformers/openai/responses/outbound.test.ts
index 37d9aac..9a6a9da 100644
--- a/src/server/transformers/openai/responses/outbound.test.ts
+++ b/src/server/transformers/openai/responses/outbound.test.ts
@@ -109,6 +109,47 @@ describe('serializeResponsesFinalPayload', () => {
     expect(payload).not.toHaveProperty('output_text');
   });
 
+  it('serializes response mode with created_at instead of created', () => {
+    const payload = serializeResponsesFinalPayload({
+      upstreamPayload: {
+        id: 'chatcmpl_response_mode',
+        object: 'chat.completion',
+        created: 1700000000,
+        model: 'gpt-5',
+        choices: [
+          {
+            index: 0,
+            finish_reason: 'stop',
+            message: {
+              role: 'assistant',
+              content: 'hello',
+            },
+          },
+        ],
+      },
+      normalized: {
+        id: 'chatcmpl_response_mode',
+        model: 'gpt-5',
+        created: 1700000000,
+        content: 'hello',
+        reasoningContent: '',
+        finishReason: 'stop',
+        toolCalls: [],
+      },
+      usage: {
+        promptTokens: 11,
+        completionTokens: 7,
+        totalTokens: 18,
+      },
+    } as any);
+
+    expect(payload).toMatchObject({
+      object: 'response',
+      created_at: 1700000000,
+    });
+    expect(payload).not.toHaveProperty('created');
+  });
+
   it('preserves top-level chat annotations on synthetic assistant messages', () => {
     const payload = serializeResponsesFinalPayload({
       upstreamPayload: {
@@ -427,4 +468,49 @@ describe('serializeResponsesFinalPayload', () => {
       },
     ]);
   });
+
+  it('preserves image generation mime_type on synthesized response payloads', () => {
+    const payload = serializeResponsesFinalPayload({
+      upstreamPayload: {
+        id: 'resp_like_mime_1',
+        model: 'gpt-5',
+        output: [
+          {
+            id: 'img_1',
+            type: 'image_generation_call',
+            status: 'completed',
+            result: 'data:image/png;base64,final',
+            mime_type: 'image/png',
+            output_format: 'png',
+          },
+        ],
+      },
+      normalized: {
+        id: 'resp_like_mime_1',
+        model: 'gpt-5',
+        created: 1700000000,
+        content: '',
+        reasoningContent: '',
+        finishReason: 'stop',
+        toolCalls: [],
+      },
+      usage: {
+        promptTokens: 1,
+        completionTokens: 2,
+        totalTokens: 3,
+      },
+    });
+
+    expect(payload.output).toEqual([
+      {
+        id: 'img_1',
+        type: 'image_generation_call',
+        status: 'completed',
+        result: 'data:image/png;base64,final',
+        mime_type: 'image/png',
+        output_format: 'png',
+        partial_images: [],
+      },
+    ]);
+  });
 });
diff --git a/src/server/transformers/openai/responses/outbound.ts b/src/server/transformers/openai/responses/outbound.ts
index be581e8..37af024 100644
--- a/src/server/transformers/openai/responses/outbound.ts
+++ b/src/server/transformers/openai/responses/outbound.ts
@@ -220,6 +220,7 @@ function extractSyntheticOutputItemsFromUpstream(payload: unknown): ResponsesOut
           result: cloneJson(rawItem.result),
           partial_images: Array.isArray(rawItem.partial_images) ? cloneJson(rawItem.partial_images) : [],
           ...(rawItem.background !== undefined ? { background: cloneJson(rawItem.background) } : {}),
+          ...(rawItem.mime_type !== undefined ? { mime_type: cloneJson(rawItem.mime_type) } : {}),
           ...(rawItem.output_format !== undefined ? { output_format: cloneJson(rawItem.output_format) } : {}),
           ...(rawItem.quality !== undefined ? { quality: cloneJson(rawItem.quality) } : {}),
           ...(rawItem.size !== undefined ? { size: cloneJson(rawItem.size) } : {}),
@@ -418,7 +419,7 @@ export function serializeResponsesFinalPayload(input: {
   return {
     id: responseId,
     object: 'response',
-    created: normalized.created,
+    created_at: normalized.created,
     status: 'completed',
     model: normalized.model,
     output,
diff --git a/src/server/transformers/openai/responses/proxyStream.test.ts b/src/server/transformers/openai/responses/proxyStream.test.ts
index fa59cf2..f364dce 100644
--- a/src/server/transformers/openai/responses/proxyStream.test.ts
+++ b/src/server/transformers/openai/responses/proxyStream.test.ts
@@ -69,4 +69,193 @@ describe('createResponsesProxyStreamSession', () => {
     expect(output).toContain('"output_text":"hello from responses upstream"');
     expect(output).toContain('data: [DONE]');
   });
+
+  it('preserves the canonical [DONE] terminator after an explicit response.completed SSE event', async () => {
+    const lines: string[] = [];
+    let ended = false;
+    const usage = {
+      promptTokens: 5,
+      completionTokens: 3,
+      totalTokens: 8,
+      cacheReadTokens: 0,
+      cacheCreationTokens: 0,
+      promptTokensIncludeCache: null,
+    };
+    const chunk = [
+      'event: response.completed',
+      'data: {"type":"response.completed","response":{"id":"resp_stream_1","model":"gpt-5","usage":{"input_tokens":5,"output_tokens":3,"total_tokens":8}}}',
+      '',
+      'data: [DONE]',
+      '',
+    ].join('\n');
+
+    const reader = {
+      reads: 0,
+      async read() {
+        if (this.reads > 0) return { done: true };
+        this.reads += 1;
+        return { done: false, value: new TextEncoder().encode(chunk) };
+      },
+      async cancel() {
+        return undefined;
+      },
+      releaseLock() {},
+    };
+
+    const session = createResponsesProxyStreamSession({
+      modelName: 'gpt-5',
+      successfulUpstreamPath: '/v1/responses',
+      getUsage: () => usage,
+      writeLines: (nextLines) => {
+        lines.push(...nextLines);
+      },
+      writeRaw: () => {},
+    });
+
+    const result = await session.run(reader as any, {
+      end() {
+        ended = true;
+      },
+    });
+
+    expect(result).toEqual({
+      status: 'completed',
+      errorMessage: null,
+    });
+    expect(ended).toBe(true);
+    const output = lines.join('');
+    expect(output).toContain('event: response.completed');
+    expect(output).toContain('data: [DONE]');
+  });
+
+  it('preserves response.incomplete SSE terminals instead of coercing them to response.failed', async () => {
+    const lines: string[] = [];
+    let ended = false;
+    const usage = {
+      promptTokens: 5,
+      completionTokens: 3,
+      totalTokens: 8,
+      cacheReadTokens: 0,
+      cacheCreationTokens: 0,
+      promptTokensIncludeCache: null,
+    };
+    const chunk = [
+      'event: response.incomplete',
+      'data: {"type":"response.incomplete","response":{"id":"resp_incomplete_1","model":"gpt-5","status":"incomplete","incomplete_details":{"reason":"max_output_tokens"},"usage":{"input_tokens":5,"output_tokens":3,"total_tokens":8}}}',
+      '',
+      'data: [DONE]',
+      '',
+    ].join('\n');
+
+    const reader = {
+      reads: 0,
+      async read() {
+        if (this.reads > 0) return { done: true };
+        this.reads += 1;
+        return { done: false, value: new TextEncoder().encode(chunk) };
+      },
+      async cancel() {
+        return undefined;
+      },
+      releaseLock() {},
+    };
+
+    const session = createResponsesProxyStreamSession({
+      modelName: 'gpt-5',
+      successfulUpstreamPath: '/v1/responses',
+      getUsage: () => usage,
+      writeLines: (nextLines) => {
+        lines.push(...nextLines);
+      },
+      writeRaw: () => {},
+    });
+
+    const result = await session.run(reader as any, {
+      end() {
+        ended = true;
+      },
+    });
+
+    expect(result).toEqual({
+      status: 'completed',
+      errorMessage: null,
+    });
+    expect(ended).toBe(true);
+    const output = lines.join('');
+    expect(output).toContain('event: response.incomplete');
+    expect(output).toContain('"status":"incomplete"');
+    expect(output).toContain('"incomplete_details":{"reason":"max_output_tokens"}');
+    expect(output).not.toContain('event: response.failed');
+    expect(output).toContain('data: [DONE]');
+  });
+
+  it('preserves non-SSE incomplete fallback payloads as response.incomplete', () => {
+    const lines: string[] = [];
+    let ended = false;
+    const usage = {
+      promptTokens: 5,
+      completionTokens: 3,
+      totalTokens: 8,
+      cacheReadTokens: 0,
+      cacheCreationTokens: 0,
+      promptTokensIncludeCache: null,
+    };
+    const payload = {
+      id: 'resp_incomplete_fallback_1',
+      object: 'response',
+      status: 'incomplete',
+      incomplete_details: {
+        reason: 'max_output_tokens',
+      },
+      model: 'gpt-5.2',
+      output_text: 'partial answer',
+      output: [
+        {
+          id: 'msg_incomplete_1',
+          type: 'message',
+          role: 'assistant',
+          status: 'incomplete',
+          content: [{ type: 'output_text', text: 'partial answer' }],
+        },
+      ],
+      usage: {
+        input_tokens: usage.promptTokens,
+        output_tokens: usage.completionTokens,
+        total_tokens: usage.totalTokens,
+      },
+    };
+
+    const session = createResponsesProxyStreamSession({
+      modelName: 'gpt-5.2',
+      successfulUpstreamPath: '/v1/responses',
+      getUsage: () => usage,
+      writeLines: (nextLines) => {
+        lines.push(...nextLines);
+      },
+      writeRaw: () => {},
+    });
+
+    const result = session.consumeUpstreamFinalPayload(
+      payload,
+      JSON.stringify(payload),
+      {
+        end() {
+          ended = true;
+        },
+      },
+    );
+
+    expect(result).toEqual({
+      status: 'completed',
+      errorMessage: null,
+    });
+    expect(ended).toBe(true);
+
+    const output = lines.join('');
+    expect(output).toContain('event: response.incomplete');
+    expect(output).toContain('"status":"incomplete"');
+    expect(output).toContain('"output_text":"partial answer"');
+    expect(output).not.toContain('event: response.completed');
+    expect(output).toContain('data: [DONE]');
+  });
 });
diff --git a/src/server/transformers/openai/responses/proxyStream.ts b/src/server/transformers/openai/responses/proxyStream.ts
index 3f0e67d..56f1f30 100644
--- a/src/server/transformers/openai/responses/proxyStream.ts
+++ b/src/server/transformers/openai/responses/proxyStream.ts
@@ -119,6 +119,7 @@ export function createResponsesProxyStreamSession(input: ResponsesProxyStreamSes
     || input.successfulUpstreamPath.endsWith('/responses')
     || input.successfulUpstreamPath.endsWith('/responses/compact');
   let finalized = false;
+  let terminalEventSeen = false;
   let terminalResult: ResponsesProxyStreamResult = {
     status: 'completed',
     errorMessage: null,
@@ -145,8 +146,6 @@ export function createResponsesProxyStreamSession(input: ResponsesProxyStreamSes
   };
 
   const complete = () => {
-    if (finalized) return;
-    finalized = true;
     terminalResult = {
       status: 'completed',
       errorMessage: null,
@@ -155,6 +154,10 @@ export function createResponsesProxyStreamSession(input: ResponsesProxyStreamSes
 
   const closeOut = () => {
     if (finalized) return;
+    if (terminalEventSeen) {
+      finalize();
+      return;
+    }
     if (requiresExplicitTerminalEvent) {
       fail({
         type: 'response.failed',
@@ -190,15 +193,14 @@ export function createResponsesProxyStreamSession(input: ResponsesProxyStreamSes
     const isFailureEvent = (
       eventBlock.event === 'error'
       || eventBlock.event === 'response.failed'
-      || eventBlock.event === 'response.incomplete'
       || payloadType === 'error'
       || payloadType === 'response.failed'
-      || payloadType === 'response.incomplete'
     );
     if (isFailureEvent) {
       fail(parsedPayload);
       return true;
     }
+    const isIncompleteEvent = eventBlock.event === 'response.incomplete' || payloadType === 'response.incomplete';
 
     if (parsedPayload && typeof parsedPayload === 'object') {
       const normalizedEvent = openAiResponsesStream.normalizeEvent(parsedPayload, streamContext, input.modelName);
@@ -225,7 +227,8 @@ export function createResponsesProxyStreamSession(input: ResponsesProxyStreamSes
         return true;
       }
       input.writeLines(convertedLines);
-      if (eventBlock.event === 'response.completed' || payloadType === 'response.completed') {
+      if (eventBlock.event === 'response.completed' || payloadType === 'response.completed' || isIncompleteEvent) {
+        terminalEventSeen = true;
         complete();
       }
       return false;
@@ -249,6 +252,9 @@ export function createResponsesProxyStreamSession(input: ResponsesProxyStreamSes
       const payloadType = (isRecord(payload) && typeof payload.type === 'string')
         ? payload.type
         : '';
+      const payloadStatus = isRecord(payload) && typeof payload.status === 'string'
+        ? payload.status
+        : '';
       if (payloadType === 'error' || payloadType === 'response.failed') {
         fail(payload);
         response?.end();
@@ -266,7 +272,8 @@ export function createResponsesProxyStreamSession(input: ResponsesProxyStreamSes
         usage: input.getUsage(),
         serializationMode: 'response',
       });
-      if (shouldFailEmptyResponsesCompletion({
+      const isIncompletePayload = payloadType === 'response.incomplete' || payloadStatus === 'incomplete';
+      if (!isIncompletePayload && shouldFailEmptyResponsesCompletion({
         payload: { type: 'response.completed', response: streamPayload },
         state: responsesState,
         usage: input.getUsage(),
@@ -287,16 +294,29 @@ export function createResponsesProxyStreamSession(input: ResponsesProxyStreamSes
         output_text: '',
       };
 
-      finalized = true;
-      terminalResult = {
-        status: 'completed',
-        errorMessage: null,
-      };
-      input.writeLines([
-        `event: response.created\ndata: ${JSON.stringify({ type: 'response.created', response: createdPayload })}\n\n`,
-        `event: response.completed\ndata: ${JSON.stringify({ type: 'response.completed', response: streamPayload })}\n\n`,
-        'data: [DONE]\n\n',
-      ]);
+      if (isIncompletePayload) {
+        finalized = true;
+        terminalResult = {
+          status: 'completed',
+          errorMessage: null,
+        };
+        input.writeLines([
+          `event: response.created\ndata: ${JSON.stringify({ type: 'response.created', response: createdPayload })}\n\n`,
+          `event: response.incomplete\ndata: ${JSON.stringify({ type: 'response.incomplete', response: streamPayload })}\n\n`,
+          'data: [DONE]\n\n',
+        ]);
+      } else {
+        finalized = true;
+        terminalResult = {
+          status: 'completed',
+          errorMessage: null,
+        };
+        input.writeLines([
+          `event: response.created\ndata: ${JSON.stringify({ type: 'response.created', response: createdPayload })}\n\n`,
+          `event: response.completed\ndata: ${JSON.stringify({ type: 'response.completed', response: streamPayload })}\n\n`,
+          'data: [DONE]\n\n',
+        ]);
+      }
       response?.end();
       return terminalResult;
     },
diff --git a/src/server/transformers/openai/responses/stream.ts b/src/server/transformers/openai/responses/stream.ts
index 7d4da3e..4e50bc3 100644
--- a/src/server/transformers/openai/responses/stream.ts
+++ b/src/server/transformers/openai/responses/stream.ts
@@ -46,6 +46,7 @@ export const openAiResponsesStream = {
     'response.image_generation_call.partial_image',
     'response.image_generation_call.completed',
     'response.completed',
+    'response.incomplete',
     'response.failed',
   ] as const,
   createContext(modelName: string): StreamTransformContext {
diff --git a/src/server/transformers/shared/chatFormatsCore.ts b/src/server/transformers/shared/chatFormatsCore.ts
index e3f0401..97b0645 100644
--- a/src/server/transformers/shared/chatFormatsCore.ts
+++ b/src/server/transformers/shared/chatFormatsCore.ts
@@ -437,6 +437,34 @@ function parseResponsesOutputText(payload: Record<string, unknown>): string {
   return parts.join('\n\n');
 }
 
+function parseResponsesReasoning(payload: Record<string, unknown>): {
+  reasoningContent: string;
+  reasoningSignature?: string;
+} {
+  const output = Array.isArray(payload.output) ? payload.output : [];
+  const reasoningParts: string[] = [];
+  let reasoningSignature = '';
+
+  for (const item of output) {
+    if (!isRecord(item)) continue;
+    if (asTrimmedString(item.type).toLowerCase() !== 'reasoning') continue;
+
+    const parsed = extractTextAndReasoning(item.summary ?? item.content ?? item);
+    const text = joinNonEmpty([parsed.content, parsed.reasoning]);
+    if (text) reasoningParts.push(text);
+
+    const encrypted = asTrimmedString(item.encrypted_content);
+    if (!reasoningSignature && encrypted) {
+      reasoningSignature = encrypted;
+    }
+  }
+
+  return {
+    reasoningContent: joinNonEmpty(reasoningParts),
+    ...(reasoningSignature ? { reasoningSignature } : {}),
+  };
+}
+
 function stringifyUnknownValue(value: unknown): string {
   if (typeof value === 'string') return value;
   if (value === undefined || value === null) return '';
@@ -658,6 +686,98 @@ function collapseOpenAiContentBlocks(
   return text || null;
 }
 
+function pickPositiveInteger(value: unknown): number | undefined {
+  if (typeof value === 'number' && Number.isFinite(value) && value > 0) {
+    return Math.trunc(value);
+  }
+  if (typeof value === 'string') {
+    const parsed = Number.parseInt(value, 10);
+    if (Number.isFinite(parsed) && parsed > 0) return parsed;
+  }
+  return undefined;
+}
+
+function convertClaudeToolsToOpenAiChat(rawTools: unknown): unknown {
+  if (!Array.isArray(rawTools)) return rawTools;
+
+  return rawTools.map((item) => {
+    if (!isRecord(item)) return item;
+
+    const type = asTrimmedString(item.type).toLowerCase();
+    if (type === 'function' || type === 'custom' || type === 'image_generation') {
+      return item;
+    }
+
+    const name = asTrimmedString(item.name);
+    if (!name) return item;
+
+    return {
+      type: 'function',
+      function: {
+        name,
+        ...(asTrimmedString(item.description)
+          ? { description: asTrimmedString(item.description) }
+          : {}),
+        parameters: isRecord(item.input_schema)
+          ? item.input_schema
+          : (isRecord(item.parameters) ? item.parameters : { type: 'object' }),
+      },
+    };
+  });
+}
+
+function convertClaudeToolChoiceToOpenAiChat(rawToolChoice: unknown): unknown {
+  if (rawToolChoice === undefined) return undefined;
+  if (typeof rawToolChoice === 'string') {
+    const normalized = rawToolChoice.trim().toLowerCase();
+    if (normalized === 'any') return 'required';
+    return normalized || rawToolChoice;
+  }
+  if (!isRecord(rawToolChoice)) return rawToolChoice;
+
+  const type = asTrimmedString(rawToolChoice.type).toLowerCase();
+  if (type === 'auto' || type === 'none') return type;
+  if (type === 'any' || type === 'required') return 'required';
+  if (type === 'function' && isRecord(rawToolChoice.function)) {
+    const name = asTrimmedString(rawToolChoice.function.name);
+    return name
+      ? {
+        type: 'function',
+        function: { name },
+      }
+      : 'required';
+  }
+  if (type !== 'tool') return rawToolChoice;
+
+  const name = asTrimmedString(
+    rawToolChoice.name
+    ?? (isRecord(rawToolChoice.tool) ? rawToolChoice.tool.name : undefined),
+  );
+  return name
+    ? {
+      type: 'function',
+      function: { name },
+    }
+    : 'required';
+}
+
+function extractClaudeReasoningRequest(
+  body: Record<string, unknown>,
+): { reasoningEffort?: string; reasoningBudget?: number } {
+  const thinking = isRecord(body.thinking) ? body.thinking : null;
+  const outputConfig = isRecord(body.output_config) ? body.output_config : null;
+  const reasoningEffort = asTrimmedString(outputConfig?.effort).toLowerCase();
+  const reasoningBudget = pickPositiveInteger(
+    thinking?.budget_tokens
+    ?? thinking?.budgetTokens,
+  );
+
+  return {
+    ...(reasoningEffort ? { reasoningEffort } : {}),
+    ...(reasoningBudget !== undefined ? { reasoningBudget } : {}),
+  };
+}
+
 function convertClaudeRequestToOpenAiBody(body: Record<string, unknown>): {
   model: string;
   stream: boolean;
@@ -717,6 +837,7 @@ function convertClaudeRequestToOpenAiBody(body: Record<string, unknown>): {
     // - user.tool_result    -> tool messages with tool_call_id
     const contentBlocks: Array<Record<string, unknown>> = [];
     const toolCalls: Array<Record<string, unknown>> = [];
+    const reasoningParts: string[] = [];
 
     const flushContentAsMessage = () => {
       const contentPayload = collapseOpenAiContentBlocks(contentBlocks);
@@ -730,7 +851,6 @@ function convertClaudeRequestToOpenAiBody(body: Record<string, unknown>): {
       const blockType = typeof block.type === 'string' ? block.type : '';
 
       if (blockType === 'tool_result') {
-        flushContentAsMessage();
         appendToolResultMessage(block.tool_use_id, block.content);
         continue;
       }
@@ -758,13 +878,18 @@ function convertClaudeRequestToOpenAiBody(body: Record<string, unknown>): {
         continue;
       }
 
+      const extracted = extractTextAndReasoning(block);
+      if (mappedRole === 'assistant' && extracted.reasoning) {
+        reasoningParts.push(extracted.reasoning);
+      }
+
       const contentBlock = toOpenAiContentBlockFromClaudeBlock(block);
       if (contentBlock) {
         contentBlocks.push(contentBlock);
         continue;
       }
 
-      const text = parseClaudeMessageContent(block);
+      const text = extracted.content || parseClaudeMessageContent(block);
       if (text) {
         contentBlocks.push({
           type: 'text',
@@ -780,11 +905,20 @@ function convertClaudeRequestToOpenAiBody(body: Record<string, unknown>): {
         tool_calls: toolCalls,
       };
       assistantMessage.content = merged || '';
+      const reasoningContent = joinNonEmpty(reasoningParts);
+      if (reasoningContent) assistantMessage.reasoning_content = reasoningContent;
       messages.push(assistantMessage);
-    } else if (merged !== null) {
-      messages.push({
+    } else if (merged !== null || (mappedRole === 'assistant' && reasoningParts.length > 0)) {
+      const nextMessage: Record<string, unknown> = {
         role: mappedRole,
-        content: merged,
+        content: merged ?? '',
+      };
+      if (mappedRole === 'assistant') {
+        const reasoningContent = joinNonEmpty(reasoningParts);
+        if (reasoningContent) nextMessage.reasoning_content = reasoningContent;
+      }
+      messages.push({
+        ...nextMessage,
       });
     }
   }
@@ -801,6 +935,8 @@ function convertClaudeRequestToOpenAiBody(body: Record<string, unknown>): {
   const topP = pickFiniteNumber(body.top_p);
   if (topP !== undefined) payload.top_p = topP;
 
+  if (isRecord(body.metadata)) payload.metadata = body.metadata;
+
   const maxTokens = pickFiniteNumber(body.max_tokens);
   if (maxTokens !== undefined) {
     payload.max_tokens = maxTokens;
@@ -812,8 +948,12 @@ function convertClaudeRequestToOpenAiBody(body: Record<string, unknown>): {
     payload.stop = body.stop_sequences;
   }
 
-  if (body.tools !== undefined) payload.tools = body.tools;
-  if (body.tool_choice !== undefined) payload.tool_choice = body.tool_choice;
+  const reasoningRequest = extractClaudeReasoningRequest(body);
+  if (reasoningRequest.reasoningEffort) payload.reasoning_effort = reasoningRequest.reasoningEffort;
+  if (reasoningRequest.reasoningBudget !== undefined) payload.reasoning_budget = reasoningRequest.reasoningBudget;
+
+  if (body.tools !== undefined) payload.tools = convertClaudeToolsToOpenAiChat(body.tools);
+  if (body.tool_choice !== undefined) payload.tool_choice = convertClaudeToolChoiceToOpenAiChat(body.tool_choice);
 
   return { model, stream, messages, payload };
 }
@@ -927,12 +1067,14 @@ export function normalizeUpstreamFinalResponse(
 
   if (isRecord(payload) && ((payload as any).object === 'response' || Array.isArray((payload as any).output))) {
     const toolCalls = collectToolCallsFromResponsesPayload(payload);
+    const responsesReasoning = parseResponsesReasoning(payload);
     return {
       id: isNonEmptyString(payload.id) ? payload.id : fallbackId,
       model: isNonEmptyString(payload.model) ? payload.model : fallbackModel,
-      created: ensureIntegerTimestamp(payload.created, now),
+      created: ensureIntegerTimestamp((payload as any).created_at ?? payload.created, now),
       content: parseResponsesOutputText(payload) || (toolCalls.length > 0 ? '' : fallbackText),
-      reasoningContent: '',
+      reasoningContent: responsesReasoning.reasoningContent,
+      ...(responsesReasoning.reasoningSignature ? { reasoningSignature: responsesReasoning.reasoningSignature } : {}),
       finishReason: toolCalls.length > 0
         ? 'tool_calls'
         : (normalizeStopReason(payload.finish_reason ?? payload.status) || 'stop'),
diff --git a/src/server/transformers/shared/normalized.test.ts b/src/server/transformers/shared/normalized.test.ts
index 74069c2..6555893 100644
--- a/src/server/transformers/shared/normalized.test.ts
+++ b/src/server/transformers/shared/normalized.test.ts
@@ -5,6 +5,7 @@ import {
   fromTransformerMetadataRecord,
   normalizeStopReason,
   normalizeUpstreamFinalResponse,
+  parseDownstreamChatRequest,
   pullSseEventsWithDone,
   serializeFinalResponse,
   toTransformerMetadataRecord,
@@ -78,6 +79,185 @@ describe('shared normalized helpers', () => {
     });
   });
 
+  it('preserves responses reasoning summaries and encrypted reasoning signatures in final normalization', () => {
+    expect(normalizeUpstreamFinalResponse({
+      object: 'response',
+      id: 'resp_reasoning_1',
+      model: 'gpt-test',
+      created_at: 456,
+      output: [
+        {
+          type: 'reasoning',
+          summary: [{ type: 'summary_text', text: 'plan quietly' }],
+          encrypted_content: 'enc-1',
+        },
+        {
+          type: 'message',
+          content: [{ type: 'output_text', text: 'hello' }],
+        },
+      ],
+      status: 'completed',
+    }, 'fallback-model')).toEqual({
+      id: 'resp_reasoning_1',
+      model: 'gpt-test',
+      created: 456,
+      content: 'hello',
+      reasoningContent: 'plan quietly',
+      reasoningSignature: 'enc-1',
+      finishReason: 'stop',
+      toolCalls: [],
+    });
+  });
+
+  it('normalizes responses payloads with reasoning summaries and encrypted signatures', () => {
+    expect(normalizeUpstreamFinalResponse({
+      object: 'response',
+      id: 'resp_reasoning_1',
+      model: 'gpt-test',
+      created: 123,
+      output: [
+        {
+          type: 'reasoning',
+          encrypted_content: 'enc_1',
+          summary: [
+            { type: 'summary_text', text: 'plan quietly' },
+          ],
+        },
+      ],
+      status: 'completed',
+    }, 'fallback-model')).toEqual({
+      id: 'resp_reasoning_1',
+      model: 'gpt-test',
+      created: 123,
+      content: '',
+      reasoningContent: 'plan quietly',
+      reasoningSignature: 'enc_1',
+      finishReason: 'stop',
+      toolCalls: [],
+    });
+  });
+
+  it('maps claude tools, tool choice, metadata, and reasoning when parsing downstream requests', () => {
+    const result = parseDownstreamChatRequest({
+      model: 'gpt-5',
+      stream: true,
+      metadata: { user_id: 'user-1' },
+      thinking: {
+        type: 'enabled',
+        budget_tokens: 2048,
+      },
+      output_config: {
+        effort: 'high',
+      },
+      tools: [{
+        name: 'Glob',
+        description: 'Search files',
+        input_schema: {
+          type: 'object',
+          properties: {
+            pattern: { type: 'string' },
+          },
+          required: ['pattern'],
+        },
+      }],
+      tool_choice: {
+        type: 'tool',
+        name: 'Glob',
+      },
+      messages: [{
+        role: 'user',
+        content: 'hello',
+      }],
+    }, 'claude');
+
+    expect(result.error).toBeUndefined();
+    expect(result.value?.upstreamBody).toMatchObject({
+      model: 'gpt-5',
+      stream: true,
+      metadata: { user_id: 'user-1' },
+      reasoning_effort: 'high',
+      reasoning_budget: 2048,
+      tools: [{
+        type: 'function',
+        function: {
+          name: 'Glob',
+          description: 'Search files',
+          parameters: {
+            type: 'object',
+            properties: {
+              pattern: { type: 'string' },
+            },
+            required: ['pattern'],
+          },
+        },
+      }],
+      tool_choice: {
+        type: 'function',
+        function: {
+          name: 'Glob',
+        },
+      },
+    });
+  });
+
+  it('keeps claude thinking in reasoning_content and emits tool results before follow-up user text', () => {
+    const result = parseDownstreamChatRequest({
+      model: 'gpt-5',
+      max_tokens: 256,
+      messages: [
+        {
+          role: 'assistant',
+          content: [
+            { type: 'thinking', thinking: 'plan quietly' },
+            {
+              type: 'tool_use',
+              id: 'toolu_abc',
+              name: 'Glob',
+              input: { pattern: 'README*' },
+            },
+          ],
+        },
+        {
+          role: 'user',
+          content: [
+            {
+              type: 'tool_result',
+              tool_use_id: 'toolu_abc',
+              content: [{ type: 'text', text: '{"matches":1}' }],
+            },
+            { type: 'text', text: 'continue' },
+          ],
+        },
+      ],
+    }, 'claude');
+
+    expect(result.error).toBeUndefined();
+    expect(result.value?.upstreamBody.messages).toEqual([
+      {
+        role: 'assistant',
+        content: '',
+        reasoning_content: 'plan quietly',
+        tool_calls: [{
+          id: 'toolu_abc',
+          type: 'function',
+          function: {
+            name: 'Glob',
+            arguments: '{"pattern":"README*"}',
+          },
+        }],
+      },
+      {
+        role: 'tool',
+        tool_call_id: 'toolu_abc',
+        content: '{"matches":1}',
+      },
+      {
+        role: 'user',
+        content: 'continue',
+      },
+    ]);
+  });
+
   it('serializes normalized final responses for claude', () => {
     const normalized = {
       id: 'chatcmpl-1',