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Step 5 Preview
Claude Sonnet 5.5
Claude Sonnet 5.5 is a proprietary model from Anthropic, released Sep 28, 2026. It ranks #28 of 351 on the LMArena text leaderboard with a rating of 1473, and #1 of 27 on the Vals Index with 70.85%. It costs $2 per million input tokens and $10 per million output tokens, with a 1M-token context window.
- Developer
- Anthropic
- Released
- Sep 28, 2026
- Context window
- 1M
- Price in / out, per 1M tokens
- $2 / $10
- Weights
- Proprietary
- Inputs
- Text, Images, Files
- Reasoning
- Yes
- Tool use
- Yes
Benchmarks
| Benchmark | Score bar | Accuracy | Rank | Cost / test |
|---|---|---|---|---|
| Vals IndexVals AI | 70.85% | 1 / 27 | $18.70 | |
| Terminal-Bench 4.0Coding | 64.14% | 2 / 55 | $16.51 | |
| Vibe Code BenchCoding | 92.39% | 1 / 115 | $31.25 | |
| Code MigrationCoding | 86.88% | 1 / 28 | $43.88 | |
| Finance AgentFinance | 67.28% | 4 / 31 | $6.95 | |
| Finance IndexFinance | 64.53% | 4 / 31 | $8.33 | |
| Tax Agent BenchFinance | 41.96% | 9 / 76 | $9.25 | |
| Legal IndexLaw | 68.02% | 20 / 28 | $13.56 | |
| Legal Research BenchLaw | 48.08% | 12 / 85 | $14.83 | |
| MedCodeMedicine | 52.92% | 12 / 107 | $2 / $10 | |
| Terminal-Bench ScienceReasoning | 47.14% | 4 / 42 | $32.52 |
Vals AI, as of Oct 24, 2026.
LMArena, by category
| Leaderboard | Rating | Rank | Votes |
|---|---|---|---|
| TextLMArena | 1473 | 28 / 351 | 9K |
| CodingLMArena | 1511 | 14 / 346 | 2.1K |
| MathLMArena | 1498 | 18 / 339 | 455 |
| Creative writingLMArena | 1468 | 18 / 349 | 2.1K |
| Instruction followingLMArena | 1491 | 13 / 351 | 3K |
| Hard promptsLMArena | 1493 | 18 / 351 | 5.5K |
| Multi-turnLMArena | 1465 | 41 / 349 | 1.3K |
| Long queriesLMArena | 1495 | 13 / 330 | 3.8K |
| ExpertLMArena | 1530 | 10 / 305 | 924 |
| Legal and governmentIndustries | 1480 | 30 / 325 | 751 |
| Medicine and healthcareIndustries | 1467 | 44 / 325 | 631 |
| Business and financeIndustries | 1468 | 24 / 344 | 1.5K |
| ChineseLanguages | 1535 | 13 / 328 | 754 |
| SpanishLanguages | 1446 | 70 / 249 | 318 |
| FrenchLanguages | 1495 | 18 / 252 | 356 |
| JapaneseLanguages | 1460 | 27 / 236 | 172 |
| WebDevLMArena | 1769 | 3 / 124 | 3.8K |
| VisionLMArena | 1287 | 30 / 146 | 2.6K |
LMArena, CC BY 4.0, as of Oct 22, 2026. Where a model is rated at several effort levels, its best is shown (Claude Sonnet 5.5 (xHigh), Claude Sonnet 5.5 (High)).
Compare Claude Sonnet 5.5
Anthropic
An AI safety and research company that builds the Claude family of models, known for coding, long context and careful behaviour. Founded 2021, based in San Francisco. anthropic.com
Questions
Who makes Claude Sonnet 5.5?
Claude Sonnet 5.5 is made by Anthropic, founded 2021 and based in San Francisco.
How much does Claude Sonnet 5.5 cost?
$2 per million input tokens and $10 per million output tokens, at its provider’s list price.
What is Claude Sonnet 5.5’s context window?
1M tokens (1,000,000).
How does Claude Sonnet 5.5 rank?
#28 of 351 on LMArena’s text leaderboard, rated 1473 (95% interval 1466–1480) from 8,977 votes, as of Oct 22, 2026.
Is Claude Sonnet 5.5 open source?
No. Claude Sonnet 5.5 is proprietary and served through its provider’s API.