fix(xai): negative text_output_tokens for xAI reasoning models

[Copilot]

Background

xAI's Chat API returns completion_tokens that include both text and reasoning tokens, matching OpenAI's o1 format. The SDK was treating this value as text-only, causing incorrect calculations that resulted in negative text token counts when reasoning tokens exceeded the misinterpreted value.

Summary

Updated token calculation in convert-xai-chat-usage.ts:

• outputTokens.total: completion_tokens + reasoningTokens → completion_tokens
• outputTokens.text: completion_tokens → completion_tokens - reasoningTokens

Example:

// xAI API response
{
  completion_tokens: 95,  // includes both text (6) and reasoning (89)
  completion_tokens_details: { reasoning_tokens: 89 }
}

// Before: text = 6 - 89 = -83 ❌
// After:  text = 95 - 89 = 6 ✅

Updated test cases:

• Updated all tests in convert-xai-chat-usage.test.ts to reflect correct xAI API format where completion_tokens includes reasoning tokens
• Fixed 3 inline snapshots in xai-chat-language-model.test.ts for reasoning model tests to match the corrected token calculation

Added changeset for the @ai-sdk/xai package to ensure proper versioning.

Manual Verification

Verified with reported scenario:

• Input: completion_tokens: 95, reasoning_tokens: 89
• Output: text: 6, reasoning: 89, total: 95 (no negative values)
• All 126 tests passing (both node and edge environments)

Checklist

• Tests have been added / updated (for bug fixes / features)
• Documentation has been added / updated (for bug fixes / features)
• A patch changeset for relevant packages has been added (for bug fixes / features - run pnpm changeset in the project root)
• I have reviewed this pull request (self-review)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Negative text_output_tokens when using grok-4-fast-reasoning</issue_title>
<issue_description>### Description

I noticed that grok-4-fast-reasoning would result in a negative number in the usage field. I logged a request, here is the raw:

"{"prompt_tokens":279,"completion_tokens":6,"total_tokens":374,"prompt_tokens_details":{"text_tokens":279,"audio_tokens":0,"image_tokens":0,"cached_tokens":149},"completion_tokens_details":{"reasoning_tokens":89,"audio_tokens":0,"accepted_prediction_tokens":0,"rejected_prediction_tokens":0}}"

In the usage field, we end up with "-83" text_output_tokens which is the 6 completion tokens minus the 89 reasoning tokens. Shouldn't this actually be 6, text_output_tokens, 89 reasoning tokens, and 95 total output tokens?

AI SDK Version

"ai": "^6.0.3",
"@ai-sdk/xai": "3.0.1",

Code of Conduct

• I agree to follow this project's Code of Conduct</issue_description>

<agent_instructions>Investigate the token counting in the xai provider and update if needed.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Negative text_output_tokens when using grok-4-fast-reasoning #11487

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[lgrammel]

@copilot add a patch changeset for the @ai-sdk/xai package

[Copilot]

@copilot add a patch changeset for the @ai-sdk/xai package

Done in e9782d1. Added patch changeset for @ai-sdk/xai package.

[lgrammel]

@copilot fix failing tests in packages/xai

[Copilot]

@copilot fix failing tests in packages/xai

Fixed in e0fd0eb. Updated test snapshots for the 3 reasoning model tests to reflect the corrected token calculation. All 126 tests now passing (both node and edge).

[ghost]

⚠️ Backport to release-v5.0 created but has conflicts: #11664