Moonshot AI Kimi K2 vs OpenAI GPT-5.3-Codex — side-by-side specs.
Moonshot AI Kimi K2 | OpenAI GPT-5.3-Codex | |
|---|---|---|
| Overview | ||
| Company | Moonshot AI | OpenAI |
| Release date | Jul 11 2025 | Feb 5 2026 |
| Model type | — | — |
| Open source | Yes | No |
| Specifications | ||
Parameters | 1T | — |
Context window | 128k | — |
| Benchmarks | ||
Coding SWE-Bench VerifiedReal coding tasks pulled from open-source projects — the AI has to find and fix actual bugs. A human-checked version of the original SWE-Bench. Higher is better. | 65.8% | — |
Science GPQA DiamondGraduate-level science questions in biology, physics, and chemistry — hard enough that subject-matter PhDs score around 65%. Higher is better. | 75.1% | — |
| Timeline | ||
| Release gap | Kimi K2 shipped 209 days before GPT-5.3-Codex | |
Kimi K2 and GPT-5.3-Codex don't publish scores on any of the same benchmarks, so there's no direct head-to-head comparison. Kimi K2 shipped 209 days before GPT-5.3-Codex, so benchmark comparisons should account for the intervening progress.
Kimi K2 is an open-source / open-weight model; GPT-5.3-Codex is proprietary.
Direct benchmark comparisons are unavailable — Kimi K2 and GPT-5.3-Codex don't publish scores on any of the same benchmarks.