Grok 4.1 Fast is a lightweight, cost-optimised model from xAI with a 2 million token context window and full multimodal input support including images and files. At $0.20 input and $0.50 output per million tokens, it is among the more affordable options in the xAI family, and the context capacity is class-leading.

However, benchmark performance is limited. The intelligence index of 16.9 places it well below mid-tier models, and scores across reasoning, coding, and instruction following are modest. The agentic index of 39.1 suggests basic tool use capability but not reliable autonomous task execution. Long-context retrieval scores are also low, which partially undermines the headline context window advantage.

This model suits high-volume, lower-complexity tasks where cost and context capacity matter more than answer quality, such as document summarisation pipelines or lightweight classification at scale. Teams needing strong reasoning or reliable agentic behaviour should look to higher-tier models.

Assessed July 10, 2026

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