Grok 4 Fast
Grok 4 Fast is xAI's latest multimodal model with SOTA cost-efficiency and a 2M token context window. It comes in two flavors: non-reasoning and reasoning. Read more about the model on xAI's [news post](http://x.ai/news/grok-4-fast). Reasoning can be enabled/disabled using the `reasoning` `enabled` parameter in the API. [Learn more in our docs](https://openrouter.ai/docs/use-cases/reasoning-tokens#controlling-reasoning-tokens)
Context window
This model accepts 2M tokens in one request (~1.5M words of text).
What fits in one request
- FitsShort documentAbout 1,500 words of text
- FitsLong documentAbout 37K words of text
- FitsSmall codebaseAbout 150K words of text
- FitsFull novelAbout 375K words of text
Specifications
Context size, pricing, and release info in one place.
- Context window
- 2,000,000 tokens (2M)
- Max output tokens
- 30,000 tokens (30K)
- Speed tier
- balanced
- Provider
- Xai
- Model family
- Grok
- Release date
- Sep 2025
Capabilities
See which features this model supports, such as vision, tools, and streaming.
- Vision
- Accepts image inputs alongside text
- Supported
- Tool use
- Can call external tools and APIs
- Supported
- Function calling
- Structured function call interface
- Supported
- Extended thinking
- Shows its chain-of-thought reasoning
- Supported
- Streaming
- Returns tokens as they are generated
- Supported
- Prompt caching
- Reuse repeated prompt prefixes cheaply
- Supported
- Web search
- Can browse the web during a request
- Not supported
- Batch API
- Process many requests asynchronously
- Not supported
Best for
Jump to a guide or ranking that matches each workload.
Compare Grok 4 Fast
Open a side-by-side comparison with one click.
- Grok 4 Fast vs Amazon Titan Text Express
Grok 4 Fast has 4661% larger context window
- Grok 4 Fast vs Amazon Titan Text Lite
Grok 4 Fast has 4661% larger context window
- Grok 4 Fast vs Amazon Titan Text Premier
Grok 4 Fast has 4661% larger context window
- Grok 4 Fast vs Claude Instant
Grok 4 Fast has 1900% larger context window
- Grok 4 Fast vs Anthropic Claude
Grok 4 Fast has 1900% larger context window
- Grok 4 Fast vs Codellama 34b Instruct
Grok 4 Fast has 48728% larger context window
Frequently asked questions
Short answers about context size and how this model behaves.
More from Xai
Other models by Xai in our catalog.
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