Claude Fable 5.1 vs Claude Fable 5.5 (Leaked Checkpoint)
A direct, empirical evaluation of Claude Fable 5.1 (Anthropic) against Claude Fable 5.5 (Leaked Checkpoint) (Anthropic).
Claude Fable 5.1
Developed by Anthropic · Proprietary Frontier parameters
Full-repository software refactoring, agentic tool workflows, formal verification, and 1.5M-token needle retrieval.
Claude Fable 5.5 (Leaked Checkpoint)
Developed by Anthropic · Proprietary Frontier Dynamic Reasoner parameters
Terminal-Bench 4.0 autonomous shell execution (78.5% target), recursive self-critique, and 1.5M-token repository refactoring.
| Metric | Claude Fable 5.1 | Claude Fable 5.5 (Leaked Checkpoint) |
|---|---|---|
| SWE-bench Verified | 82.8% | 84.2% |
| MMLU-Pro | 92.4% | 94.6% |
| MATH-500 | 97.9% | 98.4% |
| Context Window | 1,500,000 tokens | 1,500,000 tokens |
| Input Pricing (per 1M) | $12.00 | $3.50 |
| Output Pricing (per 1M) | $60.00 | $17.50 |