GPT-5.1-Codex-Max and Grok 4 Fast don't publish scores on any of the same benchmarks, so there's no direct head-to-head comparison. Grok 4 Fast shipped 79 days before GPT-5.1-Codex-Max, so benchmark comparisons should account for the intervening progress.

Published specifications for these two models are limited — see each model page for the latest details.

Direct benchmark comparisons are unavailable — GPT-5.1-Codex-Max and Grok 4 Fast don't publish scores on any of the same benchmarks.