Model comparison
Claude Sonnet 5.5 vs Kimi K2 (Jul 2025)
Claude Sonnet 5.5 is the stronger model overall, scoring 61.9 to 41.2 on the Noometry Index. Kimi K2 (Jul 2025) costs 4.0× less per token, which makes it the better buy when Claude Sonnet 5.5's lead doesn't matter for your workload.
Last verified . 14 shared benchmarks.
Summary
- They share 14 benchmarks with published results for both. Claude Sonnet 5.5 scores higher in 9 categories and Kimi K2 (Jul 2025) in 0 categories; 9 gaps are clear of the uncertainty.
- The widest gap is in math, where Claude Sonnet 5.5 leads 87.9 to 42.7.
- Kimi K2 (Jul 2025) is cheaper at $0.57 / $2.30 per million input/output tokens, against $2 / $10 for Claude Sonnet 5.5.
- Claude Sonnet 5.5 accepts more context: 1M tokens versus 262K.
- Kimi K2 (Jul 2025) has downloadable open weights; the other is API-only.
Side by side
| Claude Sonnet 5.5 | Kimi K2 (Jul 2025) | |
|---|---|---|
| Provider | Anthropic | Moonshot AI |
| Noometry Index | 61.9 | 41.2 |
| Released | 2026-09-28 | 2025-07-12 |
| Weights | Proprietary | Open |
| Context window | 1M | 262K |
| Max output | 128K | 262K |
| Input $ / M tokens | $2 | $0.57 |
| Output $ / M tokens | $10 | $2.30 |
| Results tracked | 32 | 42 |
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Category by category
Coding Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 67.3 (#6), Kimi K2 (Jul 2025): 42.4 (#102)
| Benchmark | Claude Sonnet 5.5 | Kimi K2 (Jul 2025) |
|---|---|---|
| LMArena Coding | 1513 | 1399 |
| ALE-Bench | 1,819 | 597.5 |
| FrontierCode | 52.1% | — |
| SWE-bench Verified (bash only) | — | 63.4% |
| Aider Polyglot | — | 59.1% |
| CursorBench | 55.5% | — |
| LMArena WebDev | 1774 | — |
| FrontierSWE | 61.9% | — |
| SciCode | 61% | — |
| GSO | — | 4.9% |
| WeirdML | — | 42.8% |
Agentic & Tool Use Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 45.0 (#16), Kimi K2 (Jul 2025): 32.4 (#64)
| Benchmark | Claude Sonnet 5.5 | Kimi K2 (Jul 2025) |
|---|---|---|
| Terminal-Bench | — | 35.7% |
| APEX-Agents | 75.5% | — |
| Berkeley Function Calling Leaderboard | — | 59.1% |
| METR Time Horizons | — | 59.2% |
Reasoning Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 54.0 (#28), Kimi K2 (Jul 2025): 23.3 (#179)
| Benchmark | Claude Sonnet 5.5 | Kimi K2 (Jul 2025) |
|---|---|---|
| LMArena Hard Prompts | 1495 | 1384 |
| Epoch Capabilities Index | 165.03 | 146.01 |
| SimpleBench | — | 26.3% |
| Kagi LLM Benchmark | — | 64.4% |
| NYT Connections (extended) | 80.5% | — |
| CritPt | 31.4% | — |
| Mystery Game Puzzles | 65% | — |
| ForecastBench | — | 60.2 |
Math Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 87.9 (#6), Kimi K2 (Jul 2025): 42.7 (#83)
| Benchmark | Claude Sonnet 5.5 | Kimi K2 (Jul 2025) |
|---|---|---|
| LMArena Math | 1510 | 1397 |
| FrontierMath (Tiers 1-3) | 88.8% | — |
| FrontierMath Tier 4 | 80.5% | — |
| OTIS Mock AIME 2024-2025 | 100% | — |
| ProofBench | 100% | — |
| Omni-MATH | — | 65.4% |
| FrontierMath (Feb 2025 set) | — | 21.4% |
| FrontierMath Erdős | 2.9% | — |
| FrontierMath Tier 4 (v1) | — | 0% |
Knowledge Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 66.0 (#12), Kimi K2 (Jul 2025): 37.3 (#157)
| Benchmark | Claude Sonnet 5.5 | Kimi K2 (Jul 2025) |
|---|---|---|
| LMArena Expert | 1540 | 1365 |
| GPQA Diamond | 95.6% | — |
| SimpleQA Verified | 46.5% | — |
| MMLU-Pro | — | 81.9% |
| Confabulations | — | 20.4% |
| Vectara Hallucination Rate | — | 17.9% |
| GPQA (HELM) | — | 65.3% |
Multimodal Not comparable
Claude Sonnet 5.5: 51.5 (#6), Kimi K2 (Jul 2025): —
| Benchmark | Claude Sonnet 5.5 | Kimi K2 (Jul 2025) |
|---|---|---|
| LMArena Vision | 1289 | — |
| Furniture Assembly | 75% | — |
Multilingual Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 55.3 (#30), Kimi K2 (Jul 2025): 49.6 (#130)
| Benchmark | Claude Sonnet 5.5 | Kimi K2 (Jul 2025) |
|---|---|---|
| LMArena Non-English | 1452 | 1372 |
| LMArena Chinese | 1522 | 1415 |
| LMArena Russian | 1451 | 1385 |
| LMArena French | — | 1379 |
| LMArena German | — | 1387 |
| LMArena Japanese | — | 1349 |
| LMArena Korean | — | 1325 |
| LMArena Spanish | — | 1386 |
Instruction Following Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 78.3 (#11), Kimi K2 (Jul 2025): 71.1 (#156)
| Benchmark | Claude Sonnet 5.5 | Kimi K2 (Jul 2025) |
|---|---|---|
| LMArena Instruction Following | 1495 | 1348 |
| IFEval | — | 85% |
Long Context Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 45.9 (#28), Kimi K2 (Jul 2025): 41.2 (#145)
| Benchmark | Claude Sonnet 5.5 | Kimi K2 (Jul 2025) |
|---|---|---|
| LMArena Longer Query | 1498 | 1353 |
| Fiction.LiveBench | — | 66.7% |
| CL-bench | — | 17.6% |
Writing & Preference Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 66.0 (#40), Kimi K2 (Jul 2025): 62.3 (#78)
| Benchmark | Claude Sonnet 5.5 | Kimi K2 (Jul 2025) |
|---|---|---|
| LMArena Text | 1471 | 1380 |
| LMArena Creative Writing | 1465 | 1350 |
| LMArena Multi-Turn | 1474 | 1371 |
| Short-Story Creative Writing | — | 85.6% |
| EQ-Bench Creative Writing | — | 1666 |
| WildBench | — | 86.2% |
Frequently asked questions
Is Claude Sonnet 5.5 better than Kimi K2 (Jul 2025)?
Claude Sonnet 5.5 is the stronger model overall, scoring 61.9 to 41.2 on the Noometry Index. Kimi K2 (Jul 2025) costs 4.0× less per token, which makes it the better buy when Claude Sonnet 5.5's lead doesn't matter for your workload.
Which is cheaper, Claude Sonnet 5.5 or Kimi K2 (Jul 2025)?
Kimi K2 (Jul 2025) is cheaper. It lists at $0.57 per million input tokens and $2.30 per million output tokens; Claude Sonnet 5.5 lists at $2 and $10.
Is Claude Sonnet 5.5 or Kimi K2 (Jul 2025) better for coding?
Claude Sonnet 5.5 scores higher on coding benchmarks: 67.3 versus 42.4 in the Noometry coding category.
Which has the bigger context window?
Claude Sonnet 5.5 does, with 1M tokens against 262K.
How many benchmarks do Claude Sonnet 5.5 and Kimi K2 (Jul 2025) share?
14 benchmarks have published results for both models. Claude Sonnet 5.5 has 32 scored results on Noometry and Kimi K2 (Jul 2025) has 42.