Claude Sonnet 5.5 vs Kimi K3.1 Pro
Claude Sonnet 5.5 leads Kimi K3.1 Pro on coding, 87.3 to 82.2 on the Vibe Coding Index, at about the same output price ($10.00 vs $10.00 per million). Updated October 29, 2026; 33 benchmarks have a result for both.
Claude Sonnet 5.5 or Kimi K3.1 Pro: which to pick
Pick Claude Sonnet 5.5 for coding: it scores 87.3 on the Vibe Coding Index against 82.2 for Kimi K3.1 Pro.
Pick Kimi K3.1 Pro for a larger context window (1.05M against 1M tokens) and work measured by ALE-Bench or Harvey's Legal Agent Benchmark (Vals AI), where it leads.
- Shared results
- 33
- Claude Sonnet 5.5 only
- 69
- Kimi K3.1 Pro only
- 2
- Like-for-like categories
- 7 of 9
Only benchmarks that tested both models count toward a pick; a result only one model has is shown but not compared.
Which one for your work
Each card is decided by one number both models carry. Where only one has it, the card says so and makes no call.
Coding
Vibe Coding Index, six public coding benchmarks
Claude Sonnet 5.5
Claude Sonnet 5.5 scores 87.3 against 82.2.
5 and 4 benchmarks behind the scores
Intelligence
AA Intelligence Index
Claude Sonnet 5.5
Claude Sonnet 5.5 leads, 54.2 against 46.0.
Same board, both measured
Web design
Design Arena: websites
Kimi K3.1 Pro
Kimi K3.1 Pro leads, 1325 against 1322.
Same board, both measured
General
Vals Index
Claude Sonnet 5.5
Claude Sonnet 5.5 leads, 70.8% against 62.5%.
Same board, both measured
Long documents
Listed context window
Kimi K3.1 Pro
Kimi K3.1 Pro takes 1.05M tokens against 1M.
Listed by OpenRouter
Everyday cost
1K input + 500 output tokens
No call
Claude Sonnet 5.5 $0.0070, Kimi K3.1 Pro $0.0070 per turn.
List prices
At a glance
- Coding index
- Claude Sonnet 5.5 87.3 from 5 benchmarks, Kimi K3.1 Pro 82.2 from 4 benchmarks.
- Widest category
- Agentic work, 12.0 points apart on average over 9 shared benchmarks.
- Widest single gap
- LiveBench long agentic: Claude Sonnet 5.5 63.4% against Kimi K3.1 Pro 39.1%, 24.3 points apart on a 0 to 100 scale.
- Output price
- Both cost $10.00 per million output tokens.
- Context window
- Claude Sonnet 5.5 takes 1M tokens, Kimi K3.1 Pro 1.05M.
Benchmark by benchmark
First the score: boards each model leads, per category, where both have a result. Then every board, a category to a fold; bars are each result on a 0 to 100 scale, so compare the two in a row, not one row with another.
| Category | Claude Sonnet 5.5 | Bars | Kimi K3.1 Pro | Ties |
|---|---|---|---|---|
| Coding | 8 | 1 | ||
| Intelligence | 1 | 0 | ||
| Agentic work | 8 | 1 | ||
| Reasoning | 3 | 0 | ||
| Math | 1 | 0 | ||
| Web design | 3 | 4 | ||
| General | 1 | 2 | ||
| All shared boards | 25 | 8 |
CodingLike-for-likeSix of these boards feed the Vibe Coding Index81
| Benchmark | Claude Sonnet 5.5 | Kimi K3.1 Pro | Leader |
|---|---|---|---|
| LiveBench coding | 94.7% | 81.8% | Claude Sonnet 5.5 |
| LMArena WebDev | 1770 | 1695 | Claude Sonnet 5.5 |
| Terminal-Bench 4 (Vals AI) | 64.1% | 63.6% | Claude Sonnet 5.5 |
| Vibe Code Bench (Vals AI) | 92.4% | 84.9% | Claude Sonnet 5.5 |
| Code migration (Vals AI) | 69.8% | Not measured | Only Claude Sonnet 5.5 measured |
| ProgramBench (Vals AI) | 6.5% | Not measured | Only Claude Sonnet 5.5 measured |
| IOI (Vals AI) | 83.1% | 81.9% | Claude Sonnet 5.5 |
| Terminal-Bench 2.1 (Vals AI) | 83.2% | Not measured | Only Claude Sonnet 5.5 measured |
| SWE-bench Multimodal (Vals AI) | 58.3% | Not measured | Only Claude Sonnet 5.5 measured |
| CyberBench (Vals AI) | 59.6% | Not measured | Only Claude Sonnet 5.5 measured |
| SciCode | 61.0% | 60.8% | Claude Sonnet 5.5 |
| FrontierCode | 52.1% | Not measured | Only Claude Sonnet 5.5 measured |
| FrontierSWE | 61.9% | Not measured | Only Claude Sonnet 5.5 measured |
| ALE-Bench | 1819.1 | 1932.8 | Kimi K3.1 Pro |
| LMArena Text: coding | 1512 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: software and IT | 1504 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena WebDev: React | 1817 | 1701 | Claude Sonnet 5.5 |
| LMArena WebDev: HTML | 1739 | 1706 | Claude Sonnet 5.5 |
| LMArena WebDev: from an image | 1737 | Not measured | Only Claude Sonnet 5.5 measured |
| SciCode | 13.8% | Not measured | Only Claude Sonnet 5.5 measured |
| SWE-Bench Pro V2 | 95.8% | Not measured | Only Claude Sonnet 5.5 measured |
| Neither model has a result on the other 22 boards here | |||
IntelligenceLike-for-likePublic boards, shown as published, kept out of the index10
| Benchmark | Claude Sonnet 5.5 | Kimi K3.1 Pro | Leader |
|---|---|---|---|
| AA Intelligence Index | 54.2 | 46.0 | Claude Sonnet 5.5 |
| Epoch Capabilities Index | 166.2 | Not measured | Only Claude Sonnet 5.5 measured |
Agentic workLike-for-likePublic boards, shown as published, kept out of the index81
| Benchmark | Claude Sonnet 5.5 | Kimi K3.1 Pro | Leader |
|---|---|---|---|
| Design Arena: agents building web apps | 1306 | Not measured | Only Claude Sonnet 5.5 measured |
| Design Arena: agents building mobile apps | 1286 | Not measured | Only Claude Sonnet 5.5 measured |
| Design Arena: spreadsheets | 1292 | Not measured | Only Claude Sonnet 5.5 measured |
| LiveBench research | 83.6% | 77.9% | Claude Sonnet 5.5 |
| LiveBench browser | 89.3% | 75.9% | Claude Sonnet 5.5 |
| LiveBench long agentic | 63.4% | 39.1% | Claude Sonnet 5.5 |
| SREBench (Vals AI) | 30.1% | Not measured | Only Claude Sonnet 5.5 measured |
| Finance Agent (Vals AI) | 58.1% | Not measured | Only Claude Sonnet 5.5 measured |
| Tax Agent Bench (Vals AI) | 42.0% | 24.9% | Claude Sonnet 5.5 |
| Legal Research Bench (Vals AI) | 48.1% | 37.5% | Claude Sonnet 5.5 |
| Harvey's Legal Agent Benchmark (Vals AI) | 10.4% | 11.7% | Kimi K3.1 Pro |
| Excel Modeling Benchmark (Vals AI) | 75.7% | Not measured | Only Claude Sonnet 5.5 measured |
| BioMysteryBench (Vals AI) | 81.1% | 75.6% | Claude Sonnet 5.5 |
| Terminal-Bench-Science (Vals AI) | 47.1% | 31.4% | Claude Sonnet 5.5 |
| Vals Science Index | 59.1% | 44.4% | Claude Sonnet 5.5 |
| APEX-Agents | 75.5% | Not measured | Only Claude Sonnet 5.5 measured |
| SpireClimb | 1.3% | Not measured | Only Claude Sonnet 5.5 measured |
| Vending-Bench 2 | $11,165 | Not measured | Only Claude Sonnet 5.5 measured |
| Neither model has a result on the other 24 boards here | |||
ReasoningLike-for-likePublic boards, shown as published, kept out of the index30
| Benchmark | Claude Sonnet 5.5 | Kimi K3.1 Pro | Leader |
|---|---|---|---|
| LiveBench reasoning | 91.6% | 91.1% | Claude Sonnet 5.5 |
| MysteryMechanism (Vals AI) | 49.1% | 26.1% | Claude Sonnet 5.5 |
| Humanity's Last Exam (Artificial Analysis run) | 55.0% | 52.5% | Claude Sonnet 5.5 |
| GPQA Diamond (Epoch AI run) | 95.6% | Not measured | Only Claude Sonnet 5.5 measured |
| ARC-AGI | 96.5% | Not measured | Only Claude Sonnet 5.5 measured |
| ARC-AGI-2 | 83.9% | Not measured | Only Claude Sonnet 5.5 measured |
| Chess puzzles | 59.0% | Not measured | Only Claude Sonnet 5.5 measured |
| Mystery game puzzles | 65.0% | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: hard prompts | 1494 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: expert | 1527 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: hard prompts in English | 1501 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Vision: diagrams | 1329 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Vision: homework | 1331 | Not measured | Only Claude Sonnet 5.5 measured |
| Humanity's Last Exam (Scale run) | 37.5% | Not measured | Only Claude Sonnet 5.5 measured |
| Neither model has a result on the other 9 boards here | |||
MathLike-for-likePublic boards, shown as published, kept out of the index10
| Benchmark | Claude Sonnet 5.5 | Kimi K3.1 Pro | Leader |
|---|---|---|---|
| OTIS Mock AIME | 100.0% | Not measured | Only Claude Sonnet 5.5 measured |
| FrontierMath, tiers 1 to 3 | 88.8% | Not measured | Only Claude Sonnet 5.5 measured |
| FrontierMath, tier 4 | 80.5% | Not measured | Only Claude Sonnet 5.5 measured |
| ProofBench | 100.0% | 91.0% | Claude Sonnet 5.5 |
| LMArena Text: math | 1504 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: mathematical work | 1513 | Not measured | Only Claude Sonnet 5.5 measured |
| MathArena | Not measured | 59.6% | Only Kimi K3.1 Pro measured |
| Neither model has a result on the other 7 boards here | |||
KnowledgeDirectional onlyPublic boards, shown as published, kept out of the index6 boards, none shared
| Benchmark | Claude Sonnet 5.5 | Kimi K3.1 Pro | Leader |
|---|---|---|---|
| MedCode (Vals AI) | 52.9% | Not measured | Only Claude Sonnet 5.5 measured |
| SimpleQA Verified | 46.5% | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: science | 1487 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: medicine and healthcare | 1476 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: legal and government | 1485 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: business and finance | 1466 | Not measured | Only Claude Sonnet 5.5 measured |
| Neither model has a result on the other 14 boards here | |||
Web designLike-for-likePublic boards, shown as published, kept out of the index34
| Benchmark | Claude Sonnet 5.5 | Kimi K3.1 Pro | Leader |
|---|---|---|---|
| Design Arena: websites | 1322 | 1325 | Kimi K3.1 Pro |
| Design Arena: UI components | 1373 | 1400 | Kimi K3.1 Pro |
| Design Arena: game dev | 1412 | 1410 | Claude Sonnet 5.5 |
| Design Arena: data viz | 1367 | 1300 | Claude Sonnet 5.5 |
| Design Arena: 3D | 1398 | 1451 | Kimi K3.1 Pro |
| Design Arena: all code categories | 1352 | 1354 | Kimi K3.1 Pro |
| Design Arena: SVG | Not measured | 1328 | Only Kimi K3.1 Pro measured |
| LiveBench design | 85.0% | 77.8% | Claude Sonnet 5.5 |
| Neither model has a result on the other 1 board here | |||
GeneralLike-for-likePublic boards, shown as published, kept out of the index12
| Benchmark | Claude Sonnet 5.5 | Kimi K3.1 Pro | Leader |
|---|---|---|---|
| Vals Index | 70.8% | 62.5% | Claude Sonnet 5.5 |
| LiveBench data analysis | 59.5% | 79.1% | Kimi K3.1 Pro |
| Public Benefits Bench (Vals AI) | 67.2% | Not measured | Only Claude Sonnet 5.5 measured |
| SAGE (Vals AI) | 88.0% | Not measured | Only Claude Sonnet 5.5 measured |
| MedScribe (Vals AI) | 91.1% | Not measured | Only Claude Sonnet 5.5 measured |
| Long context reasoning (AA-LCR) | 82.7% | 86.3% | Kimi K3.1 Pro |
| DTBench | 97.3% | Not measured | Only Claude Sonnet 5.5 measured |
| LMCA | 68.3% | Not measured | Only Claude Sonnet 5.5 measured |
| Furniture assembly | 75.0% | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text | 1473 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: instruction following | 1492 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: creative writing | 1470 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Vision | 1287 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: English | 1484 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: non-English | 1456 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: Chinese | 1537 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: German | 1425 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: Japanese | 1457 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: French | 1498 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: Spanish | 1447 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: Russian | 1461 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: multi-turn | 1468 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: longer queries | 1494 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: writing and language | 1474 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: entertainment and media | 1460 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Vision: English | 1289 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Vision: reading text | 1297 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Vision: creative writing | 1242 | Not measured | Only Claude Sonnet 5.5 measured |
| Neither model has a result on the other 20 boards here | |||
Image generationNot comparablePublic boards, shown as published, kept out of the index0 boards, none shared
| Benchmark | Claude Sonnet 5.5 | Kimi K3.1 Pro | Leader |
|---|---|---|---|
| Neither model has a result on 5 boards here | |||
What each workload costs
Three fixed token mixes at each model's listed price, so per-token rates become a bill.
Chat turn
1K input + 500 output tokens
Same cost
Repository review
50K input + 3K output tokens
Same cost
Agent loop
200K input + 10K output tokens
Same cost
Listed OpenRouter rates, without cache or batch discounts. A workload that does not fit a model's context window would need splitting.
Specification differences
The leading value in a row is marked; a row with a missing value names no leader. Our two rows are marked in red.
| Specification | Anthropic Claude Sonnet 5.5 | MoonshotAI Kimi K3.1 Pro |
|---|---|---|
| Maker | Anthropic | Moonshot AI |
| Weights | No public weights listed | No public weights listed |
| Released | September 28, 2026 | October 23, 2026 |
| Context window | 1M | 1.05M |
| Input $/Mtok | $2.00 | $2.00 |
| Output $/Mtok | $10.00 | $10.00 |
| Coding index | 87.3 | 82.2 |
| Independent measurements behind it | 5 | 4 |
| Cost per solved task | Not computable | Not computable |
| Source | OpenRouter listing | OpenRouter listing |
Questions
Is Claude Sonnet 5.5 better than Kimi K3.1 Pro for coding?
Pick Claude Sonnet 5.5 for coding: it scores 87.3 on the Vibe Coding Index against 82.2 for Kimi K3.1 Pro. Pick Kimi K3.1 Pro for a larger context window (1.05M against 1M tokens) and work measured by ALE-Bench or Harvey's Legal Agent Benchmark (Vals AI), where it leads.
Which is cheaper, Claude Sonnet 5.5 or Kimi K3.1 Pro?
Claude Sonnet 5.5 costs $2.00 per million input tokens and $10.00 per million output tokens; Kimi K3.1 Pro costs $2.00 and $10.00. Cost per solved task is known for neither of them.
Which has the bigger context window, Claude Sonnet 5.5 or Kimi K3.1 Pro?
Kimi K3.1 Pro, with 1.05M tokens against 1M.
How many benchmarks is the Claude Sonnet 5.5 vs Kimi K3.1 Pro comparison based on?
33 benchmarks have a result for both models as of October 29, 2026. Claude Sonnet 5.5's coding index rests on 5 independent benchmarks and Kimi K3.1 Pro's on 4. Where only one model has a result, the page says so instead of naming a winner.