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 Fable 5.1 vs Claude Opus 5.5: which is smarter?
Claude Fable 5.1 has an SI-IQ of 140 and Claude Opus 5.5 has 144. The table compares them area by area using only independent benchmark results.
| Metric | Claude Fable 5.1 | Claude Opus 5.5 |
|---|---|---|
| SI-IQ | 140136–143 | 144141–148 |
| Reasoning | 137 | 146 |
| Math | 142 | 145 |
| Knowledge | 137 | 137 |
| Developer | Anthropic | Anthropic |
| Released | Sep 1, 2026 | Sep 22, 2026 |
| Access | API access | API access |
| Price in / out (USD per 1M tokens) | $10 / $50 | $4.00 / $20 |
| Benchmarks used | 8 | 8 |
Benchmarks every compared model was tested on
Raw scores as published by the evaluators.
| Benchmark | Claude Fable 5.1 | Claude Opus 5.5 |
|---|---|---|
| Chess Puzzles | 48.0% | 67.0% |
| FrontierMath Tier 4 | 87.8% | 95.0% |
| FrontierMath Tiers 1–3 | 90.2% | 91.2% |
| Furniture Assembly | 70.0% | 83.3% |
| GPQA Diamond (OpenRouter run) | 88.9% | 90.2% |
| Mystery Game Puzzles | 58.0% | 71.0% |
| OTIS Mock AIME 2024–2025 | 100.0% | 100.0% |
| SimpleQA Verified | 70.8% | 72.2% |
| τ²-bench Airline (OpenRouter run) | 79.1% | 75.6% |
The difference of 5 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); API list prices via LiteLLM's price table (MIT); each price links to the developer's pricing page; Source: OpenRouter (openrouter.ai), licensed under CC BY 4.0: reuse and republish with attribution to OpenRouter..