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-cost
index.ts
import { streamText } from 'ai'
const result = streamText({ model: 'xai/grok-4-fast-reasoning', prompt: 'Why is the sky blue?'})More models by xAI
| Model |
|---|
| 1M | 1.1s | 85tps | $1.25/M | $2.50/M | Read: $0.2/M Write: — | $5/K + input costs | — |  | 04/30/2026 | ||||
| 2M | 3.8s | 728tps | $1.25/M | $2.50/M | Read: $0.2/M Write: — | $5/K + input costs | — | | 03/11/2026 | ||||
| 2M | 0.3s | 59tps | $1.25/M | $2.50/M | Read: $0.2/M Write: — | $5/K + input costs | — |  | 03/09/2026 | ||||
| 2M | 0.5s | 211tps | $1.25/M | $2.50/M | Read: $0.2/M Write: — | $5/K + input costs | — | | 03/09/2026 | ||||
| 1M | 0.2s | 37tps | $0.20/M | $0.50/M | Read:$0.05/M Write:— | — | — | | 07/09/2025 | ||||
| 1M | 5.4s | 208tps | $0.20/M | $0.50/M | Read:$0.05/M Write:— | — | — | | 07/09/2025 |