xAI · API-only (closed weights)

Grok 4 Fast

Grok 4 Fast is an API-only (closed weights) language model from xAI, released September 19, 2025. On the Epoch Capabilities Index it scores 144.3, rank 99 of 256 rated models.

We're thrilled to present Grok 4 Fast, our latest advancement in cost-efficient reasoning models. Built on xAI’s learnings from Grok 4, Grok 4 Fast delivers frontier-level performance across Enterprise and Consumer domains—with exceptional token efficiency.

Check it against your own PC →

Lab

xAI

Released

September 19, 2025

Weights

API-only (closed weights)

Parameters

–

Context

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Price / M tokens

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Epoch ECI

144.3 #99

Benchmark results

Epoch AI has not published results for Grok 4 Fast yet. New models are usually evaluated within days to weeks.

Links

Announcement · Epoch AI benchmarks

Models with a similar score

Qwen3.5 397B-A17B · Qwen3.7-Plus · MiniMax-M3 · Claude Sonnet 4.5 · o3-pro · Qwen 3.5 Plus (hosted 397B-A17B) · o3 · Nemotron 3 Ultra

Grok 4 Fast

Benchmark results

Links

Models with a similar score

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