Claude Sonnet 5.5
ECI#8
167Claude Sonnet 5.5 is a closed-weights model from Anthropic, released September 28, 2026. It has an ECI score of 167 and ranks 8th of 240 tracked models. At the time of its release, it ranked 4th of 227 tracked models.
Claude Sonnet 5.5 vs select alternatives
| Domain | Benchmark | Claude Sonnet 5.5 | |||
|---|---|---|---|---|---|
ECI scoreBest score 173 | 167 | 169 | 169 | 159 | |
| Ranking | #8 | #4 | #3 | #23 | |
| Games | SpireClimbBest score 34% | ||||
Chess PuzzlesBest score 79% | |||||
Mystery Game PuzzlesBest score 90% | |||||
| Mathematics | FrontierMath ErdősBest score 4% | ||||
FrontierMath Tiers 1-3 (v2)Best score 95% | |||||
FrontierMath Tier 4 (v2)Best score 100% | |||||
| Multimodal | Furniture Assembly BenchmarkBest score 90% | ||||
| Software engineering | MirrorCodeBest score 98% | ||||
| World knowledge | SimpleQA VerifiedBest score 94% |
