fix(xai): support Responses API streaming events and custom_tool_call type

Add missing schema validation for xAI Responses API server-side tools:
- Add custom_tool_call type to outputItemSchema
- Make toolCallSchema fields optional for in_progress states
- Add input field for custom_tool_call (vs arguments)
- Add action field for in_progress tool execution states
- Add 12 streaming event types for tool lifecycle:
  - web_search_call: in_progress, searching, completed
  - x_search_call: in_progress, searching, completed
  - code_execution_call: in_progress, executing, completed
  - code_interpreter_call: in_progress, executing, completed

Fixes validation errors ('Invalid JSON response', 'No matching discriminator')
when using xai.responses() with xai.tools.webSearch(), xai.tools.xSearch(),
or xai.tools.codeExecution().

Tested with generateText() and streamText() across all tool types.

Author: baturyilmaz

.changeset/smooth-ravens-suffer.md

@@ -0,0 +1,5 @@
+---
+'@ai-sdk/xai': patch
+---
+
+Fix Responses API validation errors for server-side tools (web_search, x_search, code_execution). Add missing custom_tool_call type and streaming event schemas.

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

@@ -48,12 +48,15 @@ export type XaiResponsesToolCall = {
     | 'function_call'
     | 'web_search_call'
     | 'x_search_call'
-    | 'code_interpreter_call';
+    | 'code_interpreter_call'
+    | 'custom_tool_call';
   id: string;
-  call_id: string;
-  name: string;
-  arguments: string;
+  call_id?: string;
+  name?: string;
+  arguments?: string;
+  input?: string;
   status: string;
+  action?: any;
 };
 
 export type XaiResponsesTool =
@@ -105,11 +108,13 @@ const messageContentPartSchema = z.object({
 });
 
 const toolCallSchema = z.object({
-  name: z.string(),
-  arguments: z.string(),
-  call_id: z.string(),
+  name: z.string().optional(),
+  arguments: z.string().optional(),
+  input: z.string().optional(),
+  call_id: z.string().optional(),
   id: z.string(),
   status: z.string(),
+  action: z.any().optional(),
 });
 
 const outputItemSchema = z.discriminatedUnion('type', [
@@ -137,6 +142,10 @@ const outputItemSchema = z.discriminatedUnion('type', [
     type: z.literal('view_x_video_call'),
     ...toolCallSchema.shape,
   }),
+  z.object({
+    type: z.literal('custom_tool_call'),
+    ...toolCallSchema.shape,
+  }),
   z.object({
     type: z.literal('message'),
     role: z.string(),
@@ -239,6 +248,66 @@ export const xaiResponsesChunkSchema = z.union([
     annotation_index: z.number(),
     annotation: annotationSchema,
   }),
+  z.object({
+    type: z.literal('response.web_search_call.in_progress'),
+    item_id: z.string(),
+    output_index: z.number(),
+  }),
+  z.object({
+    type: z.literal('response.web_search_call.searching'),
+    item_id: z.string(),
+    output_index: z.number(),
+  }),
+  z.object({
+    type: z.literal('response.web_search_call.completed'),
+    item_id: z.string(),
+    output_index: z.number(),
+  }),
+  z.object({
+    type: z.literal('response.x_search_call.in_progress'),
+    item_id: z.string(),
+    output_index: z.number(),
+  }),
+  z.object({
+    type: z.literal('response.x_search_call.searching'),
+    item_id: z.string(),
+    output_index: z.number(),
+  }),
+  z.object({
+    type: z.literal('response.x_search_call.completed'),
+    item_id: z.string(),
+    output_index: z.number(),
+  }),
+  z.object({
+    type: z.literal('response.code_execution_call.in_progress'),
+    item_id: z.string(),
+    output_index: z.number(),
+  }),
+  z.object({
+    type: z.literal('response.code_execution_call.executing'),
+    item_id: z.string(),
+    output_index: z.number(),
+  }),
+  z.object({
+    type: z.literal('response.code_execution_call.completed'),
+    item_id: z.string(),
+    output_index: z.number(),
+  }),
+  z.object({
+    type: z.literal('response.code_interpreter_call.in_progress'),
+    item_id: z.string(),
+    output_index: z.number(),
+  }),
+  z.object({
+    type: z.literal('response.code_interpreter_call.executing'),
+    item_id: z.string(),
+    output_index: z.number(),
+  }),
+  z.object({
+    type: z.literal('response.code_interpreter_call.completed'),
+    item_id: z.string(),
+    output_index: z.number(),
+  }),
   z.object({
     type: z.literal('response.done'),
     response: xaiResponsesResponseSchema,