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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 1M tokens for complex agent workflows.

ReasoningFile InputVision (Image)Tool UseImplicit Caching
index.ts
import { streamText } from 'ai'
const result = streamText({
model: 'xai/grok-4.1-fast-reasoning',
prompt: 'Why is the sky blue?'
})
Latency

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