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Grok 4.1 Fast Reasoning

Grok 4.1 Fast Reasoning is xAI's reasoning-enabled Grok 4.1 Fast model optimized for agentic operations. It combines structured chain-of-thought reasoning with speed-optimized inference and a context window of 2M tokens for complex agent workflows.

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


const result = streamText({
  model: 'xai/grok-4.1-fast-reasoning',
  prompt: 'Why is the sky blue?'
})
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Frequently Asked Questions

  • How does Grok 4.1 Fast Reasoning differ from the non-reasoning variant?

    Grok 4.1 Fast Reasoning generates chain-of-thought reasoning traces before making decisions, improving accuracy on complex tasks at the cost of additional latency and tokens. The non-reasoning variant produces direct responses for faster throughput.

  • What is the context window for Grok 4.1 Fast Reasoning?

    2M tokens, matching the non-reasoning variant. This supports extensive agent sessions with large tool schemas and conversation histories.

  • When should I use reasoning versus non-reasoning in my agent?

    Use reasoning for complex decisions where accuracy matters (planning, ambiguous situations, high-stakes tool calls). Use non-reasoning for routine operations where speed is more valuable than analytical depth.

  • What does Grok 4.1 Fast Reasoning cost?

    Check the pricing panel on this page for today's numbers. AI Gateway tracks rates across every provider that serves Grok 4.1 Fast Reasoning.

  • How do I authenticate with Grok 4.1 Fast Reasoning through Vercel AI Gateway?

    Use your Vercel AI Gateway API key with xai/grok-4.1-fast-reasoning as the model identifier. AI Gateway manages routing and authentication automatically.

  • Can I see the reasoning traces in the response?

    Yes. The chain-of-thought traces are included in the API response. You can inspect and log the model's reasoning for debugging and auditing.

  • Does Vercel AI Gateway support Zero Data Retention for Grok 4.1 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.