diff --git a/packages/ai/src/providers/openai-responses-shared.ts b/packages/ai/src/providers/openai-responses-shared.ts
index d769ce19..11a977d5 100644
--- a/packages/ai/src/providers/openai-responses-shared.ts
+++ b/packages/ai/src/providers/openai-responses-shared.ts
@@ -178,7 +178,7 @@ export function convertResponsesMessages<TApi extends Api>(
 					const textBlock = block as TextContent;
 					const parsedSignature = parseTextSignature(textBlock.textSignature);
 					const fallbackMessageId =
-						textBlockIndex === 0 ? `pi_msg_${msgIndex}` : `pi_msg_${msgIndex}_${textBlockIndex}`;
+						textBlockIndex === 0 ? `msg_pi_${msgIndex}` : `msg_pi_${msgIndex}_${textBlockIndex}`;
 					textBlockIndex++;
 					// OpenAI requires id to be max 64 characters
 					let msgId = parsedSignature?.id;
diff --git a/packages/ai/test/openai-responses-message-id.test.ts b/packages/ai/test/openai-responses-message-id.test.ts
index 07669d8c..f675cc8e 100644
--- a/packages/ai/test/openai-responses-message-id.test.ts
+++ b/packages/ai/test/openai-responses-message-id.test.ts
@@ -42,7 +42,7 @@ describe("OpenAI Responses message ID conversion", () => {
 			)
 			.map((item) => item.id);
 
-		expect(messageIds).toEqual(["pi_msg_1", "pi_msg_1_1"]);
+		expect(messageIds).toEqual(["msg_pi_1", "msg_pi_1_1"]);
 		expect(new Set(messageIds).size).toBe(messageIds.length);
 	});
 });