Fable 5.1

Anthropic released Fable 5.1, a new AI model that sets a standard on benchmarks, scoring 52.6% on Terminal-Bench-Science 0.1 (more than double Fable 5) and 55.8% on Terminal-Bench 4.0 versus 42.0% for Fable 5. The model also offers lower costs, with cache reads 75% cheaper and overall cost reductions of 25% for typical workloads and up to 45% for agentic ones. Anthropic introduced Enterprise Frontier Safeguards (EFS) for complete privacy, rolling out in phases starting this fall, and improved safeguards, reducing benign request flags by 60% and fallback rates on biology/medical questions by 85%.

Fable 5.1 excels at complex, long-running tasks. And its research capabilities offer an early glimpse of how AI models will contribute to scientific progress. Across our benchmarks, the model sets a new standard. It scores 52.6% on Terminal-Bench-Science 0.1, more than double Fable 5. On Terminal-Bench 4.0, it scores 55.8% against 42.0% for Fable 5. As well as being capable of much higher performance than Fable 5, it can also achieve similar or better results at a much lower cost when set to lower effort levels. Cache reads with Fable 5.1 cost 75% less than Fable 5’s. This reduces the cost of the model in practice by around 25% for typical workloads, and up to 45% for highly agentic ones. We’re also introducing Enterprise Frontier Safeguards EFS , which give enterprise customers complete privacy the same as zero data retention , while still being state-of-the-art at preventing adversarial use. EFS rolls out in phases, starting this fall. Finally, we’ve improved our safeguards. Our cybersecurity safeguards now flag benign requests about 60% less often. On basic biology and medical questions, we’ve recently reduced the fallback rate by around 85%. Claude Fable 5.1 is available everywhere today. Claude Mythos 5.1, our model for cyberdefenders and life scientists, is available through trusted access programs. Read more: