diff --git a/.changeset/fuzzy-responses-reason.md b/.changeset/fuzzy-responses-reason.md
new file mode 100644
index 000000000000..b1552472d773
--- /dev/null
+++ b/.changeset/fuzzy-responses-reason.md
@@ -0,0 +1,5 @@
+---
+'@ai-sdk/open-responses': patch
+---
+
+Stream Open Responses reasoning summary text deltas as reasoning output.
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..951e808cfcb0
--- /dev/null
+++ b/packages/open-responses/src/responses/__fixtures__/openai-reasoning-summary-text.1.chunks.txt
@@ -0,0 +1,6 @@
+{"type":"response.output_item.added","sequence_number":0,"output_index":0,"item":{"id":"rs_1","type":"reasoning","summary":[]}}
+{"type":"response.reasoning_summary_text.delta","sequence_number":1,"item_id":"rs_1","output_index":0,"summary_index":0,"delta":"Think"}
+{"type":"response.reasoning_summary_text.delta","sequence_number":2,"item_id":"rs_1","output_index":0,"summary_index":0,"delta":"ing."}
+{"type":"response.reasoning_summary_text.done","sequence_number":3,"item_id":"rs_1","output_index":0,"summary_index":0,"text":"Thinking."}
+{"type":"response.output_item.done","sequence_number":4,"output_index":0,"item":{"id":"rs_1","type":"reasoning","summary":[{"type":"summary_text","text":"Thinking."}]}}
+{"type":"response.completed","sequence_number":5,"response":{"id":"resp_1","status":"completed","incomplete_details":null,"usage":{"input_tokens":1,"output_tokens":1}}}
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 199e32b9eb7c..38de1730e751 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
@@ -1052,6 +1052,51 @@ describe('OpenResponsesLanguageModel', () => {
       });
     });
 
+    it('should stream reasoning summary text deltas', async () => {
+      prepareChunksFixtureResponse('openai-reasoning-summary-text.1');
+
+      const result = await createModel().doStream({
+        prompt: TEST_PROMPT,
+      });
+
+      const parts = await convertReadableStreamToArray(result.stream);
+
+      expect(
+        parts.filter(part => part.type.startsWith('reasoning')),
+      ).toStrictEqual([
+        {
+          type: 'reasoning-start',
+          id: 'rs_1',
+        },
+        {
+          type: 'reasoning-delta',
+          id: 'rs_1',
+          delta: 'Think',
+        },
+        {
+          type: 'reasoning-delta',
+          id: 'rs_1',
+          delta: 'ing.',
+        },
+        {
+          type: 'reasoning-end',
+          id: 'rs_1',
+          providerMetadata: {
+            lmstudio: {
+              itemId: 'rs_1',
+              reasoningSummary: [
+                {
+                  type: 'summary_text',
+                  text: 'Thinking.',
+                },
+              ],
+              reasoningContent: null,
+            },
+          },
+        },
+      ]);
+    });
+
     it.each([
       {
         event: {
diff --git a/packages/open-responses/src/responses/open-responses-language-model.ts b/packages/open-responses/src/responses/open-responses-language-model.ts
index ebdf045f0bf1..413b453b5a01 100644
--- a/packages/open-responses/src/responses/open-responses-language-model.ts
+++ b/packages/open-responses/src/responses/open-responses-language-model.ts
@@ -554,8 +554,9 @@ export class OpenResponsesLanguageModel implements LanguageModelV4 {
               });
               activeReasoningId = chunk.item.id;
             } else if (
+              chunk.type === 'response.reasoning_summary_text.delta' ||
               (chunk as { type: string }).type ===
-              'response.reasoning_text.delta'
+                'response.reasoning_text.delta'
             ) {
               const reasoningChunk = chunk as {
                 item_id: string;