feat(grok): add reasoning support

[steebchen]

Summary by CodeRabbit

• New Features
  • Added reasoning capabilities to Grok-4 fast-reasoning models with optimized output configuration.

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[coderabbitai]

Walkthrough

Added reasoning: true and reasoningOutput: "omit" properties to two XAI grok model configurations (grok-4-fast-reasoning and grok-4-1-fast-reasoning) in the exported xaiModels constant. These are additive configuration changes extending the model definition shape.

Changes

Cohort / File(s)	Summary
XAI Model Configuration packages/models/src/models/xai.ts	Added reasoning: true and reasoningOutput: "omit" properties to grok-4-fast-reasoning and grok-4-1-fast-reasoning model provider entries

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

• Single file with additive configuration changes only
• Repetitive pattern (identical properties added to two models)
• No logic modifications or structural changes

Possibly related PRs

• feat(google): add reasoning and thinkingBudget support #982: Adds reasoning property to Google model provider configurations, extending the model config shape in parallel
• feat(google): enable reasoning option for more models #1162: Adds reasoning boolean field to other model provider configurations, following the same feature pattern
• feat(models): add new Grok Fast 4 model variants #897: Modifies the same XAI grok model entries (grok-4-fast-reasoning), indicating related model variant updates

Pre-merge checks and finishing touches

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'feat(grok): add reasoning support' accurately and concisely describes the main change: enabling reasoning capabilities for Grok models by adding reasoning configuration fields.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch claude/enable-grok-reasoning-013eg7iwRMfzBSG9WK5wz6Xk

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Reviewing files that changed from the base of the PR and between 5c61c9b and 1190dc2.

📒 Files selected for processing (1)

• packages/models/src/models/xai.ts (2 hunks)

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🔇 Additional comments (2)

packages/models/src/models/xai.ts (2)

264-265: Consistent implementation across reasoning models.

Good consistency—both reasoning models (grok-4-fast-reasoning and grok-4-1-fast-reasoning) receive identical reasoning and reasoningOutput properties. This maintains uniformity across the model configurations.

Note: Verification of API compatibility mentioned in the previous comment applies to this model as well.

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198-199: No changes needed — these are metadata fields, not API parameters.

The reasoning: true and reasoningOutput: "omit" fields in the ModelDefinition are internal metadata, not parameters sent to the XAI API. They serve to:

• Declare that grok-4-fast-reasoning performs internal reasoning
• Signal that reasoning output should not be expected in responses (consistent with grok models that don't expose reasoning content)
• Inform the application's response parsing logic and capability exposure

This pattern is used consistently across other providers (Anthropic, OpenAI, Z.ai). The XAI API call correctly falls through the default case in prepareRequestBody.ts and doesn't attempt to send these fields, which is the correct behavior.

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