Anthropic releases Claude Fable 5.1, with key benchmark scores doubling compared to the previous generation

On September 1, Anthropic released Claude Fable 5.1 and Claude Mythos 5.1, marking the first update to this model series since the launch of Fable 5 on June 9. Anthropic claims that the new models are the most advanced for programming and knowledge work. In the Terminal-Bench-Science 0.1 benchmark, Fable 5.1 recorded a pass rate of 52.6%, more than doubling Fable 5's 24.7% and surpassing Opus 5's 29%; in Terminal-Bench 4, Fable 5.1 scored 55.8%, higher than Fable 5's 42% and Opus 5's 52.3%.

Fable 5.1 and Mythos 5.1 share the same underlying model, differing only in their safety filters. Fable 5.1 is available to all Claude accounts, while Mythos 5.1 remains restricted to professionals vetted through Anthropic's network security verification program and life sciences verification program. In terms of pricing, Fable 5.1 charges $10 per million tokens for input and $50 for output, which is double that of Opus 5. Cache read costs have decreased by 75%, and typical workload costs can drop by about 25%, with high agentic workloads decreasing by up to 45%.