Mistral Devstral 2 (123B) vs OpenAI GPT-5.5-Pro — side-by-side specs.
Mistral Devstral 2 (123B) | OpenAI GPT-5.5-Pro | |
|---|---|---|
| Overview | ||
| Company | Mistral | OpenAI |
| Release date | Dec 9 2025 | Apr 23 2026 |
| Model type | — | — |
| Open source | Yes | No |
| Specifications | ||
Parameters | — | — |
Context window | — | — |
| Benchmarks | ||
Science reasoning GPQA Diamond | — | — |
Software engineering SWE-Bench Verified | — | — |
Multimodal understanding MMMU | — | — |
| Timeline | ||
| Release gap | Devstral 2 (123B) shipped 135 days before GPT-5.5-Pro | |
Devstral 2 (123B) and GPT-5.5-Pro do not have directly comparable benchmark scores published on GPQA Diamond, SWE-Bench Verified, or MMMU. Devstral 2 (123B) shipped 135 days before GPT-5.5-Pro, so benchmark comparisons should account for the intervening progress.
Devstral 2 (123B) is an open-source / open-weight model; GPT-5.5-Pro is proprietary.
Direct benchmark comparisons are unavailable — at least one of these models has not published scores on GPQA Diamond, SWE-Bench Verified, or MMMU.