Devstral 2 (123B) and GPT-5.1-Codex-Max don't publish scores on any of the same benchmarks, so there's no direct head-to-head comparison. GPT-5.1-Codex-Max shipped 20 days before Devstral 2 (123B), so benchmark comparisons should account for the intervening progress.

Devstral 2 (123B) is open weight, while GPT-5.1-Codex-Max is proprietary.

Direct benchmark comparisons are unavailable — Devstral 2 (123B) and GPT-5.1-Codex-Max don't publish scores on any of the same benchmarks.