Model comparison
Claude Sonnet 5.5 vs Kimi K2.5
Claude Sonnet 5.5 is the stronger model overall, scoring 61.9 to 48.1 on the Noometry Index. Kimi K2.5 costs 4.4× less per token, which makes it the better buy when Claude Sonnet 5.5's lead doesn't matter for your workload.
Last verified . 22 shared benchmarks.
Summary
- They share 22 benchmarks with published results for both. Claude Sonnet 5.5 scores higher in 9 categories and Kimi K2.5 in 1 category; 9 gaps are clear of the uncertainty.
- The widest gap is in math, where Claude Sonnet 5.5 leads 87.9 to 51.8.
- The biggest single-benchmark swing is CritPt: 31.4% for Claude Sonnet 5.5 and 3.1% for Kimi K2.5.
- Kimi K2.5 is cheaper at $0.45 / $2.25 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 K2.5 has downloadable open weights; the other is API-only.
Side by side
| Claude Sonnet 5.5 | Kimi K2.5 | |
|---|---|---|
| Provider | Anthropic | Moonshot AI |
| Noometry Index | 61.9 | 48.1 |
| Released | 2026-09-28 | 2026-01-27 |
| Weights | Proprietary | Open |
| Context window | 1M | 262K |
| Max output | 128K | 262K |
| Input $ / M tokens | $2 | $0.45 |
| Output $ / M tokens | $10 | $2.25 |
| Results tracked | 32 | 51 |
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Category by category
Coding Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 67.3 (#6), Kimi K2.5: 48.8 (#53)
| Benchmark | Claude Sonnet 5.5 | Kimi K2.5 |
|---|---|---|
| LMArena WebDev | 1774 | 1437 |
| SciCode | 61% | 49% |
| LMArena Coding | 1513 | 1474 |
| ALE-Bench | 1,819 | 821.65 |
| SWE-bench Verified | — | 73.8% |
| FrontierCode | 52.1% | — |
| SWE-bench Verified (bash only) | — | 70.8% |
| CursorBench | 55.5% | — |
| SWE-bench Multilingual | — | 67.3% |
| FrontierSWE | 61.9% | — |
| WeirdML | — | 45.6% |
Agentic & Tool Use Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 45.0 (#16), Kimi K2.5: 34.2 (#48)
| Benchmark | Claude Sonnet 5.5 | Kimi K2.5 |
|---|---|---|
| Terminal-Bench | — | 43.2% |
| APEX-Agents | 75.5% | — |
| OSWorld | — | 63.3% |
| Vending-Bench 2 | — | 1,198 |
Reasoning Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 54.0 (#28), Kimi K2.5: 31.2 (#80)
| Benchmark | Claude Sonnet 5.5 | Kimi K2.5 |
|---|---|---|
| NYT Connections (extended) | 80.5% | 69.9% |
| CritPt | 31.4% | 3.1% |
| LMArena Hard Prompts | 1495 | 1453 |
| Epoch Capabilities Index | 165.03 | 148.03 |
| ARC-AGI-2 | — | 11.8% |
| SimpleBench | — | 46.8% |
| Kagi LLM Benchmark | — | 78.5% |
| ARC-AGI-1 | — | 65.3% |
| Chess Puzzles | — | 12% |
| EnigmaEval | — | 3.4% |
| Thematic Generalization | — | 69.4% |
| Mystery Game Puzzles | 65% | — |
Math Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 87.9 (#6), Kimi K2.5: 51.8 (#53)
| Benchmark | Claude Sonnet 5.5 | Kimi K2.5 |
|---|---|---|
| OTIS Mock AIME 2024-2025 | 100% | 92.2% |
| LMArena Math | 1510 | 1470 |
| FrontierMath (Tiers 1-3) | 88.8% | — |
| FrontierMath Tier 4 | 80.5% | — |
| MathArena Final-Answer Competitions | — | 62.3% |
| ProofBench | 100% | — |
| FrontierMath (Feb 2025 set) | — | 27.9% |
| FrontierMath Erdős | 2.9% | — |
| FrontierMath Tier 4 (v1) | — | 4.2% |
Knowledge Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 66.0 (#12), Kimi K2.5: 53.6 (#56)
| Benchmark | Claude Sonnet 5.5 | Kimi K2.5 |
|---|---|---|
| GPQA Diamond | 95.6% | 87.6% |
| SimpleQA Verified | 46.5% | 34.3% |
| LMArena Expert | 1540 | 1466 |
| Humanity's Last Exam | — | 24.4% |
| Vectara Hallucination Rate | — | 14.2% |
Multimodal Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 51.5 (#6), Kimi K2.5: 41.1 (#39)
| Benchmark | Claude Sonnet 5.5 | Kimi K2.5 |
|---|---|---|
| LMArena Vision | 1289 | 1269 |
| Furniture Assembly | 75% | — |
| LMArena Document | — | 1430 |
Multilingual Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 55.3 (#30), Kimi K2.5: 53.9 (#53)
| Benchmark | Claude Sonnet 5.5 | Kimi K2.5 |
|---|---|---|
| LMArena Non-English | 1452 | 1433 |
| LMArena Chinese | 1522 | 1495 |
| LMArena Russian | 1451 | 1435 |
| LMArena French | — | 1454 |
| LMArena German | — | 1441 |
| LMArena Japanese | — | 1421 |
| LMArena Korean | — | 1410 |
| LMArena Spanish | — | 1450 |
Instruction Following Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 78.3 (#11), Kimi K2.5: 75.3 (#64)
| Benchmark | Claude Sonnet 5.5 | Kimi K2.5 |
|---|---|---|
| LMArena Instruction Following | 1495 | 1431 |
Long Context Kimi K2.5 leads
Claude Sonnet 5.5: 45.9 (#28), Kimi K2.5: 52.1 (#7)
| Benchmark | Claude Sonnet 5.5 | Kimi K2.5 |
|---|---|---|
| LMArena Longer Query | 1498 | 1445 |
| Fiction.LiveBench | — | 86.1% |
| CL-bench | — | 19.3% |
| CL-bench Life | — | 13.2% |
Writing & Preference Too close to call
Claude Sonnet 5.5: 66.0 (#40), Kimi K2.5: 65.1 (#53)
| Benchmark | Claude Sonnet 5.5 | Kimi K2.5 |
|---|---|---|
| LMArena Text | 1471 | 1445 |
| LMArena Creative Writing | 1465 | 1423 |
| LMArena Multi-Turn | 1474 | 1444 |
| EQ-Bench Creative Writing | — | 1579 |
Frequently asked questions
Is Claude Sonnet 5.5 better than Kimi K2.5?
Claude Sonnet 5.5 is the stronger model overall, scoring 61.9 to 48.1 on the Noometry Index. Kimi K2.5 costs 4.4× 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 K2.5?
Kimi K2.5 is cheaper. It lists at $0.45 per million input tokens and $2.25 per million output tokens; Claude Sonnet 5.5 lists at $2 and $10.
Is Claude Sonnet 5.5 or Kimi K2.5 better for coding?
Claude Sonnet 5.5 scores higher on coding benchmarks: 67.3 versus 48.8 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 K2.5 share?
22 benchmarks have published results for both models. Claude Sonnet 5.5 has 32 scored results on Noometry and Kimi K2.5 has 51.