Backport: fix (provider/xai): handle error chunks in responses api (#14240)

This is an automated backport of #14223 to the release-v6.0 branch. FYI
@shaper

Co-authored-by: Walter Korman <shaper@vercel.com>

Author: vercel-ai-sdk[bot]

.changeset/dirty-moles-jog.md

@@ -0,0 +1,5 @@
+---
+"@ai-sdk/xai": patch
+---
+
+fix (provider/xai): handle mid-stream error chunks

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

@@ -538,6 +538,12 @@ export const xaiResponsesChunkSchema = z.union([
       usage: xaiResponsesUsageSchema.nullish(),
     }),
   }),
+  z.object({
+    type: z.literal('error'),
+    code: z.string().nullish(),
+    message: z.string(),
+    param: z.string().nullish(),
+  }),
   z.object({
     type: z.literal('response.done'),
     response: xaiResponsesResponseSchema,

packages/xai/src/responses/xai-responses-language-model.test.ts

@@ -3061,4 +3061,45 @@ describe('XaiResponsesLanguageModel', () => {
       });
     });
   });
+
+  describe('error event handling', () => {
+    it('should emit error chunk for server error events', async () => {
+      prepareStreamChunks([
+        JSON.stringify({
+          type: 'response.created',
+          response: {
+            id: 'resp_123',
+            object: 'response',
+            model: 'grok-4-fast-non-reasoning',
+            output: [],
+          },
+        }),
+        JSON.stringify({
+          type: 'error',
+          code: null,
+          message:
+            'Service temporarily unavailable. The model did not respond to this request.',
+          param: null,
+        }),
+      ]);
+
+      const { stream } = await createModel().doStream({
+        prompt: TEST_PROMPT,
+      });
+
+      const parts = await convertReadableStreamToArray(stream);
+      const errorPart = parts.find(part => part.type === 'error');
+
+      expect(errorPart).toMatchObject({
+        type: 'error',
+        error: {
+          type: 'error',
+          code: null,
+          message:
+            'Service temporarily unavailable. The model did not respond to this request.',
+          param: null,
+        },
+      });
+    });
+  });
 });

packages/xai/src/responses/xai-responses-language-model.ts

@@ -684,6 +684,11 @@ export class XaiResponsesLanguageModel implements LanguageModelV3 {
               return;
             }
 
+            if (event.type === 'error') {
+              controller.enqueue({ type: 'error', error: event });
+              return;
+            }
+
             // Custom tool call input streaming - already handled by output_item events
             if (
               event.type === 'response.custom_tool_call_input.delta' ||