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.
import { streamText } from 'ai'
const result = streamText({ model: 'xai/grok-4-fast-reasoning', prompt: 'Why is the sky blue?'})What To Consider When Choosing a Provider
Zero Data Retention
AI Gateway does not currently support Zero Data Retention for this model. See the documentation for models that support ZDR.Authentication
AI Gateway authenticates requests using an API key or OIDC token. You do not need to manage provider credentials directly.
Chain-of-thought traces increase output token consumption. The reasoning process adds tokens that contribute to the response cost, so factor this into budget planning.
Grok 4 Fast Reasoning is faster than the full Grok 4 but slower than the non-reasoning variant. Test with representative prompts to confirm the latency meets your application requirements.
When to Use Grok 4 Fast Reasoning
Best For
Analytical tasks requiring structured reasoning:
Chain-of-thought improves answer quality without needing the full Grok 4's depth
Code review and debugging:
Step-by-step reasoning through logic helps catch issues systematically
Mathematical and scientific problem solving
At a level below competition-grade difficulty
Data analysis and interpretation:
The model needs to reason through trends, anomalies, and relationships
Agentic workflows with complex planning:
The agent benefits from reasoning through multi-step plans before acting
Consider Alternatives When
Hardest reasoning tasks:
The full Grok 4 returns measurably better accuracy on difficult problems
Simple, direct-response tasks:
The non-reasoning variant avoids unnecessary token overhead
Maximum throughput requirements:
Reasoning traces add unacceptable latency to each request
Budget-constrained workloads:
Grok 3 Fast provides adequate reasoning at lower cost
Conclusion
Grok 4 Fast Reasoning balances reasoning depth with inference speed, making it practical for production applications that benefit from chain-of-thought without tolerating the full Grok 4's latency profile. It's well-suited as a default reasoning model for teams that need analytical capabilities in interactive or semi-real-time contexts.
FAQ
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.
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.
Yes. The chain-of-thought traces appear in the response. You can inspect the model's reasoning steps and verify its analytical process.
2M tokens.
Use your Vercel AI Gateway API key with xai/grok-4-fast-reasoning as the model identifier. AI Gateway manages provider routing automatically.
Check the pricing panel on this page for today's numbers. AI Gateway tracks rates across every provider that serves 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.
