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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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Latency

P50 time to first token (TTFT) on live AI Gateway traffic, in milliseconds. View the docs for more info.