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xAI: Grok 4 Fast

Reasoning Tool Calling Attachments

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)

Providers 1
Released Aug 19, 2025
Input Modalities text, image
Output Modalities text
Tarsk Use coding

Benchmarks

23.1
Intelligence Index
19
Coding Index
41.3
Math Index

Available Providers (1)

Provider Model ID Input Cost Output Cost Context Max Output Docs
Kilo Gateway x-ai/grok-4-fast $0.20/MTok $0.50/MTok 2M 30K

Capabilities

Reasoning
Tool Calling
Attachments
Open Weights
Structured Output