From 0bd3014e07112e311966abe0acd9cf5961c5e00e Mon Sep 17 00:00:00 2001
From: ai-sdk-factory <308175966+ai-sdk-factory@users.noreply.github.com>
Date: Wed, 26 Aug 2026 15:02:33 +0000
Subject: [PATCH] reproduction (reproduced)

Co-authored-by: Gregor Martynus <39992+gr2m@users.noreply.github.com>
---
 .ai-sdk-factory/reproduction-replay.json      | 13 +++
 ...-19659-open-responses-reasoning-summary.ts | 95 +++++++++++++++++++
 ...openai-reasoning-summary-text.1.chunks.txt |  5 +
 .../open-responses-language-model.test.ts     | 28 ++++++
 4 files changed, 141 insertions(+)
 create mode 100644 .ai-sdk-factory/reproduction-replay.json
 create mode 100644 examples/ai-functions/src/reproduction/issue-19659-open-responses-reasoning-summary.ts
 create mode 100644 packages/open-responses/src/responses/__fixtures__/openai-reasoning-summary-text.1.chunks.txt

diff --git a/.ai-sdk-factory/reproduction-replay.json b/.ai-sdk-factory/reproduction-replay.json
new file mode 100644
index 000000000000..908d9ea347b8
--- /dev/null
+++ b/.ai-sdk-factory/reproduction-replay.json
@@ -0,0 +1,13 @@
+{
+  "version": 2,
+  "issueId": 19659,
+  "expectationRevision": 1,
+  "command": "pnpm -C examples/ai-functions exec tsx src/reproduction/issue-19659-open-responses-reasoning-summary.ts",
+  "artifactPaths": [
+    "examples/ai-functions/src/reproduction/issue-19659-open-responses-reasoning-summary.ts"
+  ],
+  "expectedFailure": {
+    "exitCode": 1,
+    "signal": "ISSUE_19659_REPRODUCED: expected streamed reasoning \"Thinking.\" but received \"\""
+  }
+}
diff --git a/examples/ai-functions/src/reproduction/issue-19659-open-responses-reasoning-summary.ts b/examples/ai-functions/src/reproduction/issue-19659-open-responses-reasoning-summary.ts
new file mode 100644
index 000000000000..03f4416969ab
--- /dev/null
+++ b/examples/ai-functions/src/reproduction/issue-19659-open-responses-reasoning-summary.ts
@@ -0,0 +1,95 @@
+import { createOpenResponses } from '@ai-sdk/open-responses';
+import { streamText } from 'ai';
+
+async function main() {
+  const sse = [
+    {
+      type: 'response.output_item.added',
+      output_index: 0,
+      item: { id: 'rs_1', type: 'reasoning', summary: [] },
+    },
+    {
+      type: 'response.reasoning_summary_text.delta',
+      item_id: 'rs_1',
+      output_index: 0,
+      summary_index: 0,
+      delta: 'Think',
+    },
+    {
+      type: 'response.reasoning_summary_text.delta',
+      item_id: 'rs_1',
+      output_index: 0,
+      summary_index: 0,
+      delta: 'ing.',
+    },
+    {
+      type: 'response.reasoning_summary_text.done',
+      item_id: 'rs_1',
+      output_index: 0,
+      summary_index: 0,
+      text: 'Thinking.',
+    },
+    {
+      type: 'response.output_item.done',
+      output_index: 0,
+      item: {
+        id: 'rs_1',
+        type: 'reasoning',
+        summary: [{ type: 'summary_text', text: 'Thinking.' }],
+      },
+    },
+    {
+      type: 'response.completed',
+      response: {
+        id: 'resp_1',
+        status: 'completed',
+        incomplete_details: null,
+        usage: {
+          input_tokens: 1,
+          input_tokens_details: { cached_tokens: 0 },
+          output_tokens: 1,
+          output_tokens_details: { reasoning_tokens: 1 },
+          total_tokens: 2,
+        },
+      },
+    },
+  ]
+    .map(event => `data: ${JSON.stringify(event)}\n\n`)
+    .join('');
+
+  const provider = createOpenResponses({
+    name: 'reproduction',
+    url: 'https://example.invalid/v1/responses',
+    apiKey: 'test',
+    fetch: async () =>
+      new Response(sse, {
+        headers: { 'content-type': 'text/event-stream' },
+      }),
+  });
+
+  const result = streamText({
+    model: provider('any-model'),
+    prompt: 'hi',
+  });
+
+  let streamedReasoning = '';
+
+  for await (const part of result.fullStream) {
+    if (part.type === 'reasoning-delta') {
+      streamedReasoning += part.text;
+    }
+  }
+
+  const expectedReasoning = 'Thinking.';
+
+  if (streamedReasoning !== expectedReasoning) {
+    throw new Error(
+      `ISSUE_19659_REPRODUCED: expected streamed reasoning "${expectedReasoning}" but received "${streamedReasoning}"`,
+    );
+  }
+}
+
+main().catch(error => {
+  console.error(error);
+  process.exit(1);
+});
diff --git a/packages/open-responses/src/responses/__fixtures__/openai-reasoning-summary-text.1.chunks.txt b/packages/open-responses/src/responses/__fixtures__/openai-reasoning-summary-text.1.chunks.txt
new file mode 100644
index 000000000000..3d65158d1279
--- /dev/null
+++ b/packages/open-responses/src/responses/__fixtures__/openai-reasoning-summary-text.1.chunks.txt
@@ -0,0 +1,5 @@
+{"type":"response.output_item.added","output_index":0,"item":{"id":"rs_084abd547a8ac210006a8effb672d487d2a1c772cd76b19828","type":"reasoning","summary":[]}}
+{"type":"response.reasoning_summary_text.delta","item_id":"rs_084abd547a8ac210006a8effb672d487d2a1c772cd76b19828","output_index":0,"summary_index":0,"delta":"**Providing concise arithmetic answer**"}
+{"type":"response.reasoning_summary_text.done","item_id":"rs_084abd547a8ac210006a8effb672d487d2a1c772cd76b19828","output_index":0,"summary_index":0,"text":"**Providing concise arithmetic answer**"}
+{"type":"response.output_item.done","output_index":0,"item":{"id":"rs_084abd547a8ac210006a8effb672d487d2a1c772cd76b19828","type":"reasoning","summary":[{"type":"summary_text","text":"**Providing concise arithmetic answer**"}]}}
+{"type":"response.completed","response":{"id":"resp_084abd547a8ac210006a8effb60d2887d2bc8a15bc8f8b7f1a","model":"gpt-5-mini-2025-08-07","status":"completed","incomplete_details":null,"usage":{"input_tokens":13,"input_tokens_details":{"cache_write_tokens":0,"cached_tokens":0},"output_tokens":42,"output_tokens_details":{"reasoning_tokens":0},"total_tokens":55}}}
diff --git a/packages/open-responses/src/responses/open-responses-language-model.test.ts b/packages/open-responses/src/responses/open-responses-language-model.test.ts
index 56309f0cf283..f00fdcd0c980 100644
--- a/packages/open-responses/src/responses/open-responses-language-model.test.ts
+++ b/packages/open-responses/src/responses/open-responses-language-model.test.ts
@@ -659,6 +659,34 @@ describe('OpenResponsesLanguageModel', () => {
       });
     });
 
+    it('should stream OpenAI reasoning summary text deltas', async () => {
+      prepareChunksFixtureResponse('openai-reasoning-summary-text.1');
+
+      const result = await createModel().doStream({
+        prompt: TEST_PROMPT,
+      });
+
+      const reasoningParts = (
+        await convertReadableStreamToArray(result.stream)
+      ).filter(part => part.type.startsWith('reasoning'));
+
+      expect(reasoningParts).toStrictEqual([
+        {
+          type: 'reasoning-start',
+          id: 'rs_084abd547a8ac210006a8effb672d487d2a1c772cd76b19828',
+        },
+        {
+          type: 'reasoning-delta',
+          id: 'rs_084abd547a8ac210006a8effb672d487d2a1c772cd76b19828',
+          delta: '**Providing concise arithmetic answer**',
+        },
+        {
+          type: 'reasoning-end',
+          id: 'rs_084abd547a8ac210006a8effb672d487d2a1c772cd76b19828',
+        },
+      ]);
+    });
+
     it('should not pollute Object.prototype from tool call item ids', async () => {
       const originalArgumentsDescriptor = Object.getOwnPropertyDescriptor(
         Object.prototype,