Anthropic Launches Claude Fable 5.1 and Mythos 5.1 with 75% Cheaper Cache Reads

Anthropic released two new flagship models on September 3: Claude Fable 5.1, available broadly for coding and knowledge work, and Claude Mythos 5.1, restricted to vetted cybersecurity and life sciences teams. Both share the same underlying model and significantly outperform previous generations on research and software engineering benchmarks. Fable 5.1 introduces long-horizon stable coding and a 75% reduction in the cost of cached context for persistent agents, plus new Enterprise Frontier Safeguards that let organizations keep monitoring data inside their own infrastructure. The models are live on Amazon Bedrock and the Claude Platform on AWS.