Claude Fable 5.1 vs GPT-5-Codex
Claude Fable 5.1 
GPT-5-Codex Verdict
- Claude Fable 5.1 (max) leads on quality: 70.3 vs 58.2.
- Claude Fable 5.1 (max) is stronger in agents & tools, coding, composite, human preference, knowledge, maths, reasoning.
- GPT-5-Codex is stronger in instruction following, long context, multimodal.
- GPT-5-Codex is 5.8× cheaper ($3.44 vs $20.00 per 1M blended).
| Metric | Claude Fable 5.1 (max) | GPT-5-Codex |
|---|---|---|
| BenchLeader Index | 70.3 | 58.2 |
| Agents & tools score | 67.4 | 56.3 |
| Coding score | 78.4 | 53.6 |
| Composite score | 76.6 | 60.4 |
| Human preference score | 71.3 | – |
| Knowledge score | 75.9 | 60.6 |
| Maths score | 77.0 | – |
| Reasoning score | 71.9 | 64.3 |
| Instruction following score | – | 72.1 |
| Long context score | – | 62.2 |
| Multimodal score | – | 58.2 |
| Blended price $/M | $20.00 | $3.44 |
| Output speed | 40 tok/s | – |
| Time to first answer | 299.8 s | – |
| Context window | 1M | 400k |
| FrontierMath Tiers 1–3 | 90.2% | – |
| FrontierMath Tier 4 | 87.8% | – |
| OTIS Mock AIME | 100.0% | – |
| SimpleQA Verified | 70.8% | – |
| Terminal-Bench | 57.9% | 44.3% |
| SciCode | 62.0% | – |
| WeirdML | 92.9% | 54.5% |
| ProofBench | 100.0% | – |
| LMArena Text | 1504 | – |
| LMArena Hard Prompts | 1522 | – |
| LMArena Coding | 1517 | – |
| LMArena WebDev | 1764 | – |
| LMArena Agent | 14.5 | – |
| LiveBench | 83.4% | – |
| LiveBench Reasoning | 91.7% | – |
| LiveBench Coding | 86.4% | – |
| LiveBench Agentic Coding | 66.1% | – |
| LiveBench Mathematics | 97.0% | – |
| LiveBench Data Analysis | 80.3% | – |
| LiveBench Language | 89.5% | – |
| AA Intelligence Index | – | 24.9 |
| IFBench | – | 74.2% |
| AA-LCR | – | 71.7% |
| MMMU-Pro | – | 73.8% |
| AA-Omniscience | – | -7.5 |
| Terminal-Bench Hard | – | 37.9% |
| GPQA Diamond (AA) | – | 83.7% |
| Humanity's Last Exam (AA) | – | 27.9% |
| τ²-Bench Telecom (AA) | – | 86.8% |
| Kagi LLM Benchmark | – | 70.3% |
| ARC-AGI-1 | 97.5% | – |
| ARC-AGI-2 | 90.0% | – |
Data as of 2026-09-10. Best configuration of each model; every score links to its source on the model pages.
Claude Fable 5.1 vs GPT-5-Codex: questions
- Is Claude Fable 5.1 better than GPT-5-Codex?
- Claude Fable 5.1 (max) leads on quality: 70.3 vs 58.2. The BenchLeader Index combines every independent quality benchmark; Claude Fable 5.1 (max) is ahead overall as of 2026-09-10, but check the category scores for your use.
- Is Claude Fable 5.1 better than GPT-5-Codex for coding?
- Claude Fable 5.1 scores higher in coding (78 vs 54 on the category index, where 50 is average).
- Is Claude Fable 5.1 better than GPT-5-Codex for agentic tasks?
- Claude Fable 5.1 scores higher in agentic tasks (67 vs 56 on the category index, where 50 is average).
- Which is cheaper, Claude Fable 5.1 or GPT-5-Codex?
- GPT-5-Codex is cheaper: $3.44 against $20.00 per million tokens, blended at three input tokens per output token.
- Which has the larger context window?
- Claude Fable 5.1 accepts more context: 1M against 400k tokens.