From 288015577246aab442e9e7c36033a5331ddebc77 Mon Sep 17 00:00:00 2001
From: Gioxa <barelravo@gmail.com>
Date: Mon, 11 May 2026 20:22:07 +0700
Subject: [PATCH] fix(openai-responses): emit reasoning summary as
 delta.reasoning_content (#2159)
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Integrated into release/v3.8.0 — emit reasoning summary as delta.reasoning_content for Chat Completions clients
---
 open-sse/translator/response/openai-responses.ts    | 9 +++++++--
 tests/unit/responses-translation-fixes.test.ts      | 2 +-
 tests/unit/translator-resp-openai-responses.test.ts | 2 +-
 3 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/open-sse/translator/response/openai-responses.ts b/open-sse/translator/response/openai-responses.ts
index 07ff889385..a5b5ceafdf 100644
--- a/open-sse/translator/response/openai-responses.ts
+++ b/open-sse/translator/response/openai-responses.ts
@@ -823,13 +823,18 @@ export function openaiResponsesToOpenAIResponse(chunk, state) {
     };
   }
 
-  // Handle true reasoning summary ("Thought for 15s")
+  // Handle true reasoning summary ("Thought for 15s").
+  // Emit as `delta.reasoning_content` — matches the shape used by the
+  // `reasoning_content_text.delta` branch above and is what Chat clients
+  // (OpenCode, Claude Code, Cursor, etc.) actually render in their thinking
+  // panel. A nested `delta.reasoning.summary` object is swallowed by most
+  // stream mergers and never reaches the user.
   if (eventType === "response.reasoning_summary_text.delta") {
     const reasoningDelta = data.delta || "";
     if (!reasoningDelta) return null;
     const reasoningDeltaShape = state.copilotCompatibleReasoning
       ? { reasoning_text: reasoningDelta }
-      : { reasoning: { summary: reasoningDelta } };
+      : { reasoning_content: reasoningDelta };
     return {
       id: state.chatId,
       object: "chat.completion.chunk",
diff --git a/tests/unit/responses-translation-fixes.test.ts b/tests/unit/responses-translation-fixes.test.ts
index 1abf64d3eb..644c4882a4 100644
--- a/tests/unit/responses-translation-fixes.test.ts
+++ b/tests/unit/responses-translation-fixes.test.ts
@@ -406,7 +406,7 @@ test("Responses→Chat streaming: reasoning delta emits reasoning_content in Cha
   };
   const result = openaiResponsesToOpenAIResponse(chunk, state);
   assert.ok(result, "should return a chunk");
-  assert.equal(result.choices[0].delta.reasoning.summary, "thinking step...");
+  assert.equal(result.choices[0].delta.reasoning_content, "thinking step...");
 });
 
 test("Responses→Chat streaming: Copilot mode emits reasoning_text for summary deltas", () => {
diff --git a/tests/unit/translator-resp-openai-responses.test.ts b/tests/unit/translator-resp-openai-responses.test.ts
index 78ba82d5bb..292c4b7d11 100644
--- a/tests/unit/translator-resp-openai-responses.test.ts
+++ b/tests/unit/translator-resp-openai-responses.test.ts
@@ -289,7 +289,7 @@ test("Responses -> OpenAI: tool-call delta, reasoning delta and completed usage
 
   assert.equal(added.choices[0].delta.tool_calls[0].function.name, "weather");
   assert.equal(args.choices[0].delta.tool_calls[0].function.arguments, '{"city":"SP"}');
-  assert.equal(reasoning.choices[0].delta.reasoning.summary, "Need weather info.");
+  assert.equal(reasoning.choices[0].delta.reasoning_content, "Need weather info.");
   assert.equal(completed.choices[0].finish_reason, "tool_calls");
   assert.equal((completed as any).usage.prompt_tokens, 8);
   assert.equal((completed as any).usage.completion_tokens, 2);