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xAI: Grok 4 Fast

x-ai/grok-4-fast

Released Sep 19, 2025Knowledge cutoff Sep 30, 20252,000,000 context

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(opens in new tab).

Reasoning can be enabled/disabled using the reasoning enabled parameter in the API. Learn more in our docs(opens in new tab)

Recent activity on Grok 4 Fast

Total usage per day on OpenRouter

Prompt
1.55B
Reasoning
200M
Completion
165M

Prompt tokens measure input size. Reasoning tokens show internal thinking before a response. Completion tokens reflect total output length.