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Sep 1, 2026

Anthropic releases Claude Fable 5.1, more than doubling predecessor on key benchmark

Anthropic shipped Claude Fable 5.1 and Claude Mythos 5.1 on September 1, with Fable 5.1 scoring 52.6% on Terminal-Bench-Science 0.1 compared to Fable 5's 24.7%, representing a major performance leap.

Sep 1, 2026·2 sources

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Top claims

▪Anthropic reduced API cache read costs by 75% to $0.25 per million tokens, while keeping base pricing unchanged at $10 input and $50 output per million tokens
▪The 75% reduction in API cache read costs cuts typical workload costs by roughly 25% and highly agentic workloads by up to 45%
▪Claude Fable 5.1 is generally available to anyone with a Claude account, while Claude Mythos 5.1 is restricted to vetted cybersecurity and life-sciences professionals

Topics

Large language models (LLMs)AI research & benchmarks Claude Fable 5.1 AI tools & products