Anthropic introduced Claude Fable 5.1 and Claude Mythos 5.1, its latest models for coding, knowledge work and scientific research.

Both use the same underlying model, but Fable 5.1 is generally available while Mythos 5.1 offers more permissive safeguards exclusively to vetted cybersecurity and life-sciences professionals. Anthropic says Fable 5.1 delivers stronger performance while reducing typical workload costs by roughly 25% compared with its predecessor.