Description

streamText fails with response.custom_tool_call_input.delta validation error when using xAI x_search tool

Description

When using streamText with xAI's x_search tool, the SDK throws a TypeValidationError because the xAI API returns a streaming event type (response.custom_tool_call_input.delta) that is not defined in the Zod schema.

Reproduction

import { xai } from "@ai-sdk/xai";
import { streamText } from "ai";

const result = streamText({
  model: xai.responses("grok-4-fast"),
  prompt: "What are people saying about AI on X this week?",
  tools: {
    x_search: xai.tools.xSearch({
      allowedXHandles: ["elonmusk", "xai"],
      fromDate: "2025-10-23",
      toDate: "2025-10-30",
      enableImageUnderstanding: true,
      enableVideoUnderstanding: true,
    }),
  },
});

for await (const chunk of result.textStream) {
  process.stdout.write(chunk);
}

Expected Behavior

streamText should work with x_search tool, similar to how generateText works.

Actual Behavior

Throws AI_TypeValidationError with the following value:

{
  "sequence_number": 3,
  "type": "response.custom_tool_call_input.delta",
  "item_id": "ctc_ac6aa674-1d37-2384-0ff8-ec5e0257c75d_xs_call_55111848",
  "output_index": 0,
  "delta": "{\"query\":\"AI artificial intelligence\",\"limit\":20,\"from_date\":\"2025-11-20\",\"to_date\":\"2025-11-26\",\"min_score_threshold\":0.2}"
}

Comparison

Environment

• ai: 6.0.0-beta.118
• @ai-sdk/xai: 3.0.0-beta.44
• Node.js: v22.x

Root Cause

The recent PR added custom_tool_call type to outputItemSchema, but the streaming chunk schema (xaiResponsesChunkSchema) is missing the response.custom_tool_call_input.delta event type.

Suggested Fix

Add the following to xaiResponsesChunkSchema in packages/xai/src/responses/xai-responses-api.ts:

z.object({
  type: z.literal("response.custom_tool_call_input.delta"),
  item_id: z.string(),
  output_index: z.number(),
  delta: z.string(),
}),

AI SDK Version

ai: 6.0.0-beta.118
@ai-sdk/xai: 3.0.0-beta.44
Node.js: v22.x

Code of Conduct

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