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Grok 4 Fast Reasoning

Grok 4 Fast Reasoning is the speed-optimized reasoning variant of xAI's Grok 4 Fast. It combines chain-of-thought reasoning with faster inference than the full Grok 4, within a context window of 2M tokens.

ReasoningTool UseImplicit Cachingtiered-costVision (Image)File InputWeb Search
index.ts
import { streamText } from 'ai'


const result = streamText({
  model: 'xai/grok-4-fast-reasoning',
  prompt: 'Why is the sky blue?'
})
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Frequently Asked Questions

  • What is the difference between Grok 4 Fast Reasoning and Grok 4 Fast Non-Reasoning?

    Grok 4 Fast Reasoning generates chain-of-thought reasoning traces that improve accuracy on analytical tasks. The non-reasoning variant produces direct answers at lower latency and cost.

  • How does Grok 4 Fast Reasoning compare to the full Grok 4?

    The full Grok 4 provides deeper reasoning at higher latency and cost. Grok 4 Fast Reasoning offers a faster alternative that still benefits from structured thinking on moderately complex tasks.

  • Can I see the reasoning traces in the API response?

    Yes. The chain-of-thought traces appear in the response. You can inspect the model's reasoning steps and verify its analytical process.

  • What is the context window?

    2M tokens.

  • How do I authenticate with Grok 4 Fast Reasoning through Vercel AI Gateway?

    Use your Vercel AI Gateway API key with xai/grok-4-fast-reasoning as the model identifier. AI Gateway manages provider routing automatically.

  • What does Grok 4 Fast Reasoning cost?

    Check the pricing panel on this page for today's numbers. AI Gateway tracks rates across every provider that serves Grok 4 Fast Reasoning.

  • Does Vercel AI Gateway support Zero Data Retention for Grok 4 Fast Reasoning?

    Zero Data Retention is not currently available for this model. ZDR on AI Gateway applies to direct gateway requests; BYOK flows aren't covered. See https://vercel.com/docs/ai-gateway/capabilities/zdr for details.