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xAI Released September 18, 2025 Synced Apr 19, 2026

xAI: 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...

Tool useVisionReasoning

Why it stands out

Offers a 2000K-token context window, enabling full-document and multi-file analysis without chunking.
Combines tool use with reasoning — a strong baseline for agentic and multi-step workflows.
Multimodal input (vision) extends it beyond text-only workflows.
$0.2/M input makes it practical for always-on agents, batch processing, or high-volume classification.

What to watch

No benchmark score currently tracked — evaluate using task-specific testing alongside pricing and capability data.

Release timeline

Tracked events for xAI: Grok 4 Fast.

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release

xAI: Grok 4 Fast entered the tracked catalog

September 18, 2025

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)

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Recent changes

LaunchSep 18

xAI launched xAI: Grok 4 Fast

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