Automated page. Written and translated automatically by AI and checked against the sources by software; no human editor. SI-IQ is an index built from public benchmark results, not an IQ test. How it works
Claude Opus 5.5 vs Claude Sonnet 5.5: which is smarter?
Claude Opus 5.5 has an SI-IQ of 144 and Claude Sonnet 5.5 has 140. The table compares them area by area using only independent benchmark results.
Data as of Oct 18, 2026 · method 1.0.0
| Metric | Claude Opus 5.5 | Claude Sonnet 5.5 |
|---|---|---|
| SI-IQ | 144141–148 | 140137–143 |
| Reasoning | 146 | 142 |
| Math | 145 | 140 |
| Knowledge | 137 | 137 |
| Developer | Anthropic | Anthropic |
| Released | Sep 22, 2026 | Sep 28, 2026 |
| Access | API access | API access |
| Price in / out (USD per 1M tokens) | $4.00 / $20 | $2.00 / $10 |
| Benchmarks used | 9 | 9 |
The difference of 4 points is within the statistical uncertainty: the two models are roughly on par.
Data sources: Arena leaderboard dataset on Hugging Face (CC BY 4.0); Epoch AI, ‘Capabilities & benchmarking’ (CC BY 4.0); LiteLLM, model_prices_and_context_window.json (MIT); Source: OpenRouter (openrouter.ai), licensed under CC BY 4.0: reuse and republish with attribution to OpenRouter (licences and changes).