1 vs 1 benchmarks won
Moonshot AI Kimi K2 | OpenAI GPT-5.5 | |
|---|---|---|
| Overview | ||
| Company | Moonshot AI | OpenAI |
| Release date | Jul 11 2025 | Apr 23 2026 |
| Model type | — | — |
| Open source | Yes | No |
| Specifications | ||
Parameters | 1T | — |
Context window | 128k | — |
| Benchmarks | ||
Science reasoning GPQA Diamond | 75.1% | 93.6% |
Software engineering SWE-Bench Verified | 65.8% | — |
Multimodal understanding MMMU | — | — |
| Timeline | ||
| Release gap | Kimi K2 shipped 286 days before GPT-5.5 | |
Kimi K2 and GPT-5.5 are evenly matched across the benchmarks they both publish. Kimi K2 shipped 286 days before GPT-5.5, so benchmark comparisons should account for the intervening progress.
Kimi K2 is an open-source / open-weight model; GPT-5.5 is proprietary.
On GPQA Diamond, GPT-5.5 scores 93.6%, 18.5 points above Kimi K2 at 75.1%.