Claude Sonnet 5.5
Claude Sonnet 5.5 is an API-only (closed weights) language model from Anthropic, released September 28, 2026. The context window is 1M tokens. On the Epoch Capabilities Index it scores 166.6, rank 8 of 256 rated models. API price: $2 input / $10 output per million tokens.
Introducing Claude Sonnet 5.5, the second model in the Claude 5.5 family. It’s a clear upgrade over Claude Sonnet 5, runs 30%+ faster, and costs up to 30% less for most work.
Check it against your own PC →
Strengths by category
ModelTape's 0–100 fit on Epoch AI benchmark results.
| Category | Score | Based on |
|---|---|---|
| Reasoning | 41.2 | Chess Puzzles, SimpleBench, Mystery Game Puzzles, Humanity's Last Exam |
| Math | 78.3 | ProofBench, OTIS Mock AIME 2024-2025, FrontierMath-Tiers-1-3-v2-Private, FrontierMath-Tier-4-v2-Private |
| Coding | 82.0 | MirrorCode, FrontierSWE |
| Knowledge | 76.6 | GPQA diamond, SimpleQA Verified |
Benchmark results
| Benchmark (Epoch AI) | Score |
|---|---|
| ProofBench | 100.0% |
| OTIS Mock AIME | 100.0% |
| GPQA Diamond | 98.0% |
| MirrorCode | 97.8% |
| FrontierMath (Tiers 1–3) | 93.4% |
| FrontierMath-Tier-4-v2-Private | 80.5% |
| SimpleBench | 71.1% |
| Furniture Assembly | 64.3% |
| FrontierSWE | 61.9% |
| Mystery Game Puzzles | 61.4% |
| Chess Puzzles | 56.9% |
| SimpleQA Verified | 46.5% |
| Humanity's Last Exam | 46.1% |
| SpireClimb | 1.3% |
Links
Announcement · Epoch AI benchmarks
Models with a similar score
Gemini 4 Carbon · GPT-6 Astra · Claude Opus 5.5 · GPT-6.1 Sol · GPT-6.1 Terra · Claude Fable 5.1 · Gemini 4 Argon · Claude Opus 5
More from Anthropic
Claude Fable 5.2 · Claude Haiku 5.5 · Claude Opus 5.5 · Claude Fable 5.1 · Claude Opus 5 · Claude Sonnet 5 · Claude Fable 5 · Claude Mythos 5