From 840988d6ca297cf969667903c9682d9501bb0bd3 Mon Sep 17 00:00:00 2001
From: Kazuhiro Sera <seratch@openai.com>
Date: Fri, 3 Oct 2025 12:01:29 -0700
Subject: [PATCH] fix: #562 invalid model settings when prompt is set in Agent

---
 .changeset/young-bars-hide.md                 |  5 ++++
 examples/basic/prompt-id.ts                   |  1 -
 .../agents-openai/src/openaiResponsesModel.ts |  2 +-
 .../test/openaiResponsesModel.test.ts         | 30 +++++++++++++++++++
 4 files changed, 36 insertions(+), 2 deletions(-)
 create mode 100644 .changeset/young-bars-hide.md

diff --git a/.changeset/young-bars-hide.md b/.changeset/young-bars-hide.md
new file mode 100644
index 00000000..308854dc
--- /dev/null
+++ b/.changeset/young-bars-hide.md
@@ -0,0 +1,5 @@
+---
+'@openai/agents-openai': patch
+---
+
+fix: #562 invalid model settings when prompt is set in Agent
diff --git a/examples/basic/prompt-id.ts b/examples/basic/prompt-id.ts
index 94c77281..a318836c 100644
--- a/examples/basic/prompt-id.ts
+++ b/examples/basic/prompt-id.ts
@@ -5,7 +5,6 @@ async function main() {
     name: 'Assistant',
     prompt: {
       promptId: 'pmpt_68d50b26524c81958c1425070180b5e10ab840669e470fc7',
-      version: '1',
       variables: { name: 'Kaz' },
     },
   });
diff --git a/packages/agents-openai/src/openaiResponsesModel.ts b/packages/agents-openai/src/openaiResponsesModel.ts
index 772a74d7..dd6916d1 100644
--- a/packages/agents-openai/src/openaiResponsesModel.ts
+++ b/packages/agents-openai/src/openaiResponsesModel.ts
@@ -878,7 +878,7 @@ export class OpenAIResponsesModel implements Model {
     }
 
     const requestData = {
-      model: this.#model,
+      ...(!request.prompt ? { model: this.#model } : {}),
       instructions: normalizeInstructions(request.systemInstructions),
       input,
       include,
diff --git a/packages/agents-openai/test/openaiResponsesModel.test.ts b/packages/agents-openai/test/openaiResponsesModel.test.ts
index 5d33d76b..b5f37367 100644
--- a/packages/agents-openai/test/openaiResponsesModel.test.ts
+++ b/packages/agents-openai/test/openaiResponsesModel.test.ts
@@ -74,6 +74,36 @@ describe('OpenAIResponsesModel', () => {
     });
   });
 
+  it('omits model when a prompt is provided', async () => {
+    await withTrace('test', async () => {
+      const fakeResponse = { id: 'res-prompt', usage: {}, output: [] };
+      const createMock = vi.fn().mockResolvedValue(fakeResponse);
+      const fakeClient = {
+        responses: { create: createMock },
+      } as unknown as OpenAI;
+      const model = new OpenAIResponsesModel(fakeClient, 'gpt-default');
+
+      const request = {
+        systemInstructions: undefined,
+        prompt: { promptId: 'pmpt_123' },
+        input: 'hello',
+        modelSettings: {},
+        tools: [],
+        outputType: 'text',
+        handoffs: [],
+        tracing: false,
+        signal: undefined,
+      };
+
+      await model.getResponse(request as any);
+
+      expect(createMock).toHaveBeenCalledTimes(1);
+      const [args] = createMock.mock.calls[0];
+      expect('model' in args).toBe(false);
+      expect(args.prompt).toMatchObject({ id: 'pmpt_123' });
+    });
+  });
+
   it('normalizes systemInstructions so empty strings are omitted', async () => {
     await withTrace('test', async () => {
       const fakeResponse = {