Anthropic Unveils Claude Fable 5.1 and Mythos 5.1 With Cheaper, Sharper Performance

Anthropic announced Claude Fable 5.1 and Mythos 5.1, boasting improved coding, knowledge-work and long-running problem solving, while offering roughly 25% lower costs on typical workloads (up to 45% for highly agentic tasks) thanks to cheaper cache reads; Fable 5.1 is generally available and Mythos 5.1 is accessible through trusted access programs, with Mythos tailored for cybersecurity and life sciences; Millennium testing reportedly helped identify a rare internal crash that stumped engineers.