Claude Sonnet 5.5
ECI#4
165Claude Sonnet 5.5 is a closed-weights model from Anthropic, released September 28, 2026. It has an ECI score of 165 and ranks 4th of 257 tracked models. At the time of its release, it ranked 3rd of 256 tracked models.
Claude Sonnet 5.5 vs select alternatives
| Domain | Benchmark | Claude Sonnet 5.5 | |||
|---|---|---|---|---|---|
ECI scoreBest score 167 | 165 | 167 | 166 | 157 | |
| Ranking | #4 | #1 – Best | #2 | #15 | |
| Games | Mystery Game PuzzlesBest score 84% | ||||
| Mathematics | FrontierMath Tiers 1-3 (v2)Best score 94% | ||||
FrontierMath Tier 4 (v2)Best score 100% | |||||
OTIS Mock AIME 2024-2025Best score 100% | |||||
| Multimodal | Furniture Assembly BenchmarkBest score 83% | ||||
| Science | GPQA DiamondBest score 96% | ||||
| Software engineering | Text Arena (Coding)Best score 1820 | 1786 | 1820 | 1800 | 1674 |
WeirdML (v3)Best score 42% | |||||
| World knowledge | SimpleQA VerifiedBest score 76% |
