Gemma 4 and GPT-5-Codex-Mini don't publish scores on any of the same benchmarks, so there's no direct head-to-head comparison. GPT-5-Codex-Mini shipped 145 days before Gemma 4, so benchmark comparisons should account for the intervening progress.

Gemma 4 is open weight, while GPT-5-Codex-Mini is proprietary.

Direct benchmark comparisons are unavailable — Gemma 4 and GPT-5-Codex-Mini don't publish scores on any of the same benchmarks.