Claude Sonnet 5.5
ECI#6
166Claude Sonnet 5.5 is a closed-weights model from Anthropic, released September 28, 2026. It has an ECI score of 166 and ranks 6th of 253 tracked models. At the time of its release, it ranked 4th of 247 tracked models.
Claude Sonnet 5.5 vs select alternatives
| Domain | Benchmark | Claude Sonnet 5.5 | |||
|---|---|---|---|---|---|
ECI scoreBest score 169 | 166 | 169 | 169 | 158 | |
| Ranking | #6 | #1 – Best | #2 | #18 | |
| Games | SpireClimbBest score 26% | ||||
Chess PuzzlesBest score 76% | |||||
Mystery Game PuzzlesBest score 84% | |||||
| Mathematics | FrontierMath ErdősBest score 4% | ||||
FrontierMath Tiers 1-3 (v2)Best score 94% | |||||
FrontierMath Tier 4 (v2)Best score 100% | |||||
| Multimodal | Furniture Assembly BenchmarkBest score 83% | ||||
| Science | GPQA DiamondBest score 96% | ||||
| World knowledge | SimpleQA VerifiedBest score 76% |
