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Step 5 Preview
Claude Opus 5.5
Claude Opus 5.5 is a proprietary model from Anthropic, released Sep 22, 2026. It ranks #2 of 351 on the LMArena text leaderboard with a rating of 1516, and #2 of 27 on the Vals Index with 70.18%. It costs $4 per million input tokens and $20 per million output tokens, with a 1M-token context window.
- Developer
- Anthropic
- Released
- Sep 22, 2026
- Context window
- 1M
- Price in / out, per 1M tokens
- $4 / $20
- Weights
- Proprietary
- Inputs
- Text, Images, Files
- Reasoning
- Yes
- Tool use
- Yes
Benchmarks
| Benchmark | Score bar | Accuracy | Rank | Cost / test |
|---|---|---|---|---|
| Vals IndexVals AI | 70.18% | 2 / 27 | $28.12 | |
| Terminal-Bench 4.0Coding | 65.15% | 1 / 55 | $13.20 | |
| Vibe Code BenchCoding | 90.29% | 5 / 115 | $57.92 | |
| Code MigrationCoding | 81.01% | 2 / 28 | $72.40 | |
| Finance AgentFinance | 67.85% | 1 / 31 | $8.91 | |
| Finance IndexFinance | 65.59% | 1 / 31 | $11.67 | |
| Tax Agent BenchFinance | 45.57% | 3 / 76 | $15.09 | |
| Legal IndexLaw | 72.33% | 7 / 28 | $20.54 | |
| Legal Research BenchLaw | 50.48% | 7 / 85 | $25.16 | |
| MedCodeMedicine | 49.80% | 19 / 107 | $4 / $20 | |
| Terminal-Bench ScienceReasoning | 47.14% | 3 / 42 | $19.12 |
Vals AI, as of Oct 24, 2026.
LMArena, by category
| Leaderboard | Rating | Rank | Votes |
|---|---|---|---|
| TextLMArena | 1516 | 2 / 351 | 10.3K |
| CodingLMArena | 1545 | 1 / 346 | 2.3K |
| MathLMArena | 1518 | 6 / 339 | 535 |
| Creative writingLMArena | 1534 | 1 / 349 | 2.5K |
| Instruction followingLMArena | 1539 | 1 / 351 | 3.6K |
| Hard promptsLMArena | 1536 | 2 / 351 | 6.4K |
| Multi-turnLMArena | 1504 | 8 / 349 | 1.4K |
| Long queriesLMArena | 1533 | 2 / 330 | 4.4K |
| ExpertLMArena | 1550 | 3 / 305 | 1.1K |
| Legal and governmentIndustries | 1516 | 4 / 325 | 888 |
| Medicine and healthcareIndustries | 1512 | 4 / 325 | 711 |
| Business and financeIndustries | 1497 | 5 / 344 | 1.8K |
| ChineseLanguages | 1581 | 3 / 328 | 927 |
| SpanishLanguages | 1509 | 3 / 249 | 372 |
| FrenchLanguages | 1493 | 21 / 252 | 379 |
| JapaneseLanguages | 1535 | 2 / 236 | 193 |
| WebDevLMArena | 1807 | 1 / 124 | 3.1K |
| VisionLMArena | 1321 | 2 / 146 | 3K |
LMArena, CC BY 4.0, as of Oct 22, 2026. Where a model is rated at several effort levels, its best is shown (Claude Opus 5.5 (High), Claude Opus 5.5 (Max)).
Compare Claude Opus 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 Opus 5.5?
Claude Opus 5.5 is made by Anthropic, founded 2021 and based in San Francisco.
How much does Claude Opus 5.5 cost?
$4 per million input tokens and $20 per million output tokens, at its provider’s list price.
What is Claude Opus 5.5’s context window?
1M tokens (1,000,000).
How does Claude Opus 5.5 rank?
#2 of 351 on LMArena’s text leaderboard, rated 1516 (95% interval 1509–1523) from 10,322 votes, as of Oct 22, 2026.
Is Claude Opus 5.5 open source?
No. Claude Opus 5.5 is proprietary and served through its provider’s API.