X-Ai/Grok-4-Fast-Reasoning

X-Ai/Grok-4-Fast-Reasoning

Developer	xAI
Release date	December 18, 2025
Family	Grok
Generation	Grok 4
Level
Context window	2M tokens
Max output	2M tokens
Input	Text, image, audio, video
Output	Text
Weights	Closed
Successor	Grok 4.1 Fast (Reasoning)
Website	x.ai
Links	Model card Docs

Part of a series on

Context: 2Mtokens
Released: 10mo ago

Specifications

Model

Developer: xAI
Family: Grok Grok 4
Type: Language model
Released: December 18, 2025
Model ID: xai/grok-4-fast-reasoning

Capabilities

Input → output: Text, image, audio, video → Text
Max output: 2M tokens

Weights

Openness: Closed

Sources:models.dev

Metadata synced Nov 3, 2026, 11:17 PM UTC

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