fix: preserve assistant reasoning when replaying Open Responses output in tool loops

.changeset/calm-dogs-reason.md

@@ -0,0 +1,5 @@
+---
+"@ai-sdk/open-responses": patch
+---
+
+Preserve assistant reasoning parts when converting prompts to Open Responses input.

packages/open-responses/src/responses/convert-to-open-responses-input.test.ts

@@ -359,6 +359,35 @@ describe('convertToOpenResponsesInput', () => {
         ]
       `);
     });
+
+    it('should convert reasoning parts to reasoning items', async () => {
+      const result = await convertToOpenResponsesInput({
+        prompt: [
+          {
+            role: 'assistant',
+            content: [
+              {
+                type: 'reasoning',
+                text: 'Analyzing the problem step by step',
+              },
+            ],
+          },
+        ],
+      });
+
+      expect(result.input).toEqual([
+        {
+          type: 'reasoning',
+          summary: [],
+          content: [
+            {
+              type: 'reasoning_text',
+              text: 'Analyzing the problem step by step',
+            },
+          ],
+        },
+      ]);
+    });
   });
 
   describe('assistant messages with tool calls', () => {

packages/open-responses/src/responses/convert-to-open-responses-input.ts

@@ -16,6 +16,7 @@ import type {
   InputTextContentParam,
   OpenResponsesRequestBody,
   OutputTextContentParam,
+  ReasoningItemParam,
   RefusalContentParam,
 } from './open-responses-api';
 
@@ -105,10 +106,19 @@ export async function convertToOpenResponsesInput({
         const assistantContent: Array<
           OutputTextContentParam | RefusalContentParam
         > = [];
+        const reasoningItems: Array<ReasoningItemParam> = [];
         const toolCalls: Array<FunctionCallItemParam> = [];
 
         for (const part of content) {
           switch (part.type) {
+            case 'reasoning': {
+              reasoningItems.push({
+                type: 'reasoning',
+                summary: [],
+                content: [{ type: 'reasoning_text', text: part.text }],
+              });
+              break;
+            }
             case 'text': {
               assistantContent.push({ type: 'output_text', text: part.text });
               break;
@@ -129,6 +139,11 @@ export async function convertToOpenResponsesInput({
           }
         }
 
+        // Push reasoning as separate items
+        for (const reasoningItem of reasoningItems) {
+          input.push(reasoningItem);
+        }
+
         // Push assistant message with text content if any
         if (assistantContent.length > 0) {
           input.push({

packages/open-responses/src/responses/open-responses-api.ts

@@ -143,7 +143,7 @@ export type ReasoningItemParam = {
   id?: string;
   type: 'reasoning';
   summary: ReasoningSummaryContentParam[];
-  content?: unknown;
+  content?: ReasoningTextContent[];
   encrypted_content?: string;
 };