Anthropic releases Claude Fable 5.1 and Claude Mythos 5.1
Claude Fable 5.1 is available now, while Claude Mythos 5.1 for cyberdefenders and life scientists is available through trusted access programs.
- Fable 5.1 scores 52.6% on Terminal-Bench-Science 0.1 and 55.8% on Terminal-Bench 4.0.
- Cache reads cost 75% less than Fable 5, cutting practical costs by 25% for typical workloads and up to 45% for agentic tasks.
- Cybersecurity safeguards flag benign requests 60% less often, and biology fallback rates dropped by about 85%.
- Enterprise Frontier Safeguards with zero data retention will roll out in phases starting this fall.
Developers and researchers get more capable reasoning and coding models with reduced caching costs and fewer false-positive safety refusals.
