Moonshot AI Kimi K2 (0905) vs xAI Grok 4 Fast — side-by-side specs.
Moonshot AI Kimi K2 (0905) | xAI Grok 4 Fast | |
|---|---|---|
| Overview | ||
| Company | Moonshot AI | xAI |
| Release date | Sep 5 2025 | Sep 2025 |
| Model type | — | — |
| Open source | Yes | No |
| Specifications | ||
Parameters | 1T | — |
Context window | 256k | — |
| 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 | Grok 4 Fast shipped 4 days before Kimi K2 (0905) | |
Kimi K2 (0905) and Grok 4 Fast don't publish scores on any of the same benchmarks, so there's no direct head-to-head comparison. Grok 4 Fast shipped 4 days before Kimi K2 (0905), so benchmark comparisons should account for the intervening progress.
Kimi K2 (0905) is an open-source / open-weight model; Grok 4 Fast is proprietary.
Direct benchmark comparisons are unavailable — Kimi K2 (0905) and Grok 4 Fast don't publish scores on any of the same benchmarks.