Claude Opus 4.8 vs Kimi K2 (0905)
Anthropic Claude Opus 4.8 | Moonshot AI Kimi K2 (0905) | |
|---|---|---|
| Overview | ||
| Company | Anthropic | Moonshot AI |
| Release date | May 28 2026 | Sep 5 2025 |
| Access | Proprietary | Open Weight |
| Specifications | ||
Parameters | — | 1T |
Context window | 1M | 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. | 95% | — |
Agentic coding SWE-Bench ProCan the AI fix real bugs in real software? It's handed actual problems from open-source projects and has to write code that genuinely solves them. Higher is better. | 69.2% | — |
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% |
Multilingual coding SWE-Bench MultilingualLike SWE-Bench, but the coding problems span many programming languages, not just one. Tests how broadly the AI can code. Higher is better. | 84.4% | — |
Agentic coding CursorBench v3.1Cursor's own test of harder, real-world coding tasks inside a code editor. Higher is better. | 63.8% | — |
Agentic coding DeepSWE 1.0Artificial Analysis' independent test of deep, agentic software-engineering work — the AI has to plan and carry out substantial coding tasks end to end. Higher is better. | 55.8% | — |
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. | 88% | — |
Agentic terminal coding Terminal-Bench 2.1Can the AI work in a command-line terminal — running commands and finishing technical setup tasks the way a developer would? Higher is better. | 74.6% | — |
Web browsing BrowseCompCan the AI browse the web and track down hard-to-find answers? Higher is better. | 84.3% | — |
Multidisciplinary reasoning Humanity's Last Exam · no toolsHumanity's Last Exam — extremely hard expert questions across many subjects, written so you can't just look up the answer. “No tools” means the AI answers on its own. Higher is better. | 49.8% | — |
Multidisciplinary reasoning Humanity's Last Exam · with toolsHumanity's Last Exam — extremely hard expert questions across many subjects. “With tools” means the AI is allowed to search the web or run code while answering. Higher is better. | 57.9% | — |
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% |
Agentic computer use OSWorld-VerifiedCan the AI actually operate a computer — clicking, typing, and using real apps — to finish tasks on its own? Higher is better. | 83.4% | — |
Agentic financial analysis Finance Agent v2Tests the AI on real financial-analysis work, like digging through reports and making sound decisions. Higher is better. | 53.9% | — |
Agentic legal work Harvey's Legal Agent BenchmarkHarvey's test of whether an AI agent can complete real legal work — drafting and reviewing documents, working with spreadsheets and presentations, and navigating files the way a lawyer's assistant would. Higher is better. | 9.58% | — |
Tax questions TaxEval v2A set of real tax questions created by Vals AI — can the AI give accurate answers about tax rules and filings? Higher is better. | 75.63% | — |
Medical admin work MedScribeCan the AI support doctors with their administrative work, like notes and paperwork? Created by Vals AI. Higher is better. | 85.75% | — |
Knowledge work GDPval-AAMeasures how well the AI does economically valuable knowledge work, judged against human experts. Shown as a rating (like a chess Elo) — higher is better. | 1890 | — |
Community preference Arena Elo (Text)Real people chat with two anonymous AIs side by side and vote for the answer they prefer. Votes become a chess-style Elo rating on arena.ai — it measures which AI people actually like, not test scores. Higher is better. | 1482 | — |
Community preference (code) Arena Elo (Code)Like the text arena, but people vote on which AI writes better code. The votes become a chess-style Elo rating on arena.ai. Higher is better. | 1560 | — |
| Timeline | ||
| Release gap | Kimi K2 (0905) shipped 265 days before Claude Opus 4.8 | |
Which is better: Claude Opus 4.8 or Kimi K2 (0905)?
Claude Opus 4.8 and Kimi K2 (0905) don't publish scores on any of the same benchmarks, so there's no direct head-to-head comparison. Kimi K2 (0905) shipped 265 days before Claude Opus 4.8, so benchmark comparisons should account for the intervening progress.
Context windows are 1M (Claude Opus 4.8) vs 256k (Kimi K2 (0905)). Claude Opus 4.8 is proprietary, while Kimi K2 (0905) is open weight.
Direct benchmark comparisons are unavailable — Claude Opus 4.8 and Kimi K2 (0905) don't publish scores on any of the same benchmarks.
Frequently asked questions
Claude Opus 4.8 was released by Anthropic on May 28 2026.
Kimi K2 (0905) was released by Moonshot AI on Sep 5 2025.
Claude Opus 4.8 has a 1M context window; Kimi K2 (0905) has 256k.
Claude Opus 4.8 is a proprietary model released by Anthropic. Kimi K2 (0905) is an open weight model released by Moonshot AI.
Other comparisons
Claude Opus 4.8 vs GPT-5.6 SolKimi K2 (0905) vs GPT-5.6 SolClaude Opus 4.8 vs Gemini OmniKimi K2 (0905) vs Gemini OmniClaude Opus 4.8 vs Muse Spark 1.1Kimi K2 (0905) vs Muse Spark 1.1Claude Opus 4.8 vs Grok 4.5Kimi K2 (0905) vs Grok 4.5Claude Opus 4.8 vs DeepSeek-V4-ProKimi K2 (0905) vs DeepSeek-V4-ProClaude Opus 4.8 vs Mistral Medium 3.5Kimi K2 (0905) vs Mistral Medium 3.5