Claude Sonnet 4.5 vs Kimi K2 (0905)
Anthropic Claude Sonnet 4.5 | Moonshot AI Kimi K2 (0905) | |
|---|---|---|
| Overview | ||
| Company | Anthropic | Moonshot AI |
| Release date | Sep 29 2025 | Sep 5 2025 |
| Access | Proprietary | Open Weight |
| Specifications | ||
Parameters | — | 1T |
Context window | — | 256k |
| Benchmarks | ||
Nonsense detection BullshitBench v2Given a confidently-worded but nonsensical prompt, does the AI spot that it makes no sense and push back — instead of playing along and inventing an answer? The score is how often it clearly called out the nonsense. Higher is better. | 79% | — |
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. | 77.2%Best | 65.8% |
Next.js coding Next.js EvalsVercel's open eval of how well AI coding agents build and migrate real Next.js apps — measured as the share of tasks the agent completes successfully. Higher is better. | 50% | — |
Science GPQA DiamondGraduate-level science questions in biology, physics, and chemistry — hard enough that subject-matter PhDs score around 65%. Higher is better. | 83.4%Best | 75.1% |
Multimodal MMMUTests the AI on understanding images and text together across many college subjects. Higher is better. | 68% | — |
| Timeline | ||
| Release gap | Kimi K2 (0905) shipped 24 days before Claude Sonnet 4.5 | |
Which is better: Claude Sonnet 4.5 or Kimi K2 (0905)?
Claude Sonnet 4.5 leads Kimi K2 (0905) on 2 of the 2 benchmarks they both report (SWE-Bench Verified, GPQA Diamond). Kimi K2 (0905) shipped 24 days before Claude Sonnet 4.5, so benchmark comparisons should account for the intervening progress.
Claude Sonnet 4.5 is proprietary, while Kimi K2 (0905) is open weight.
On SWE-Bench Verified, Claude Sonnet 4.5 leads at 77.2% vs Kimi K2 (0905) at 65.8%. On GPQA Diamond, Claude Sonnet 4.5 leads at 83.4% vs Kimi K2 (0905) at 75.1%.
Frequently asked questions
Claude Sonnet 4.5 was released by Anthropic on Sep 29 2025.
Kimi K2 (0905) was released by Moonshot AI on Sep 5 2025.
Claude Sonnet 4.5 leads on SWE-Bench Verified — Claude Sonnet 4.5 77.2% vs Kimi K2 (0905) 65.8%.
Claude Sonnet 4.5 leads on GPQA Diamond — Claude Sonnet 4.5 83.4% vs Kimi K2 (0905) 75.1%.
Claude Sonnet 4.5 is a proprietary model released by Anthropic. Kimi K2 (0905) is an open weight model released by Moonshot AI.