Devstral 2 (123B) and GPT-5.6 Luna don't publish scores on any of the same benchmarks, so there's no direct head-to-head comparison. Devstral 2 (123B) shipped 199 days before GPT-5.6 Luna, so benchmark comparisons should account for the intervening progress.

Devstral 2 (123B) is open weight, while GPT-5.6 Luna is proprietary.

Direct benchmark comparisons are unavailable — Devstral 2 (123B) and GPT-5.6 Luna don't publish scores on any of the same benchmarks.