Background

Add inputCachedTokens to xai provider.

Summary

Include the cached_tokens variable as part of the inputCachedTokens.

Part of grok-4-fast response

      "usage": {
        "prompt_tokens": 2640,
        "completion_tokens": 182,
        "total_tokens": 3494,
        "prompt_tokens_details": {
          "text_tokens": 2640,
          "audio_tokens": 0,
          "image_tokens": 0,
          "cached_tokens": 473
        },
        "completion_tokens_details": {
          "reasoning_tokens": 672,
          "audio_tokens": 0,
          "accepted_prediction_tokens": 0,
          "rejected_prediction_tokens": 0
        },
        "num_sources_used": 0
      }

Manual Verification

• pnpm build in this repo
• Installed ai sdk 6.0.0-beta.68
• Used generated package with grok-4-fast
• .usage variable

{
  inputTokens: 555,
  outputTokens: 190,
  totalTokens: 1802,
  reasoningTokens: 1057,
  cachedInputTokens: 316,
}

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)

Future Work

N/A

Related Issues

N/A