Introducing Claude Fable 5.1 and Claude Mythos 5.1

Anthropic has announced Claude Fable 5.1 and Claude Mythos 5.1, which are the same advanced model with different safeguard levels. Fable 5.1 is generally available for coding and knowledge work, while Mythos 5.1 is a restricted version for cybersecurity and life sciences via trusted access programs. Key improvements include a significant price reduction (up to 45% for agentic work), enhanced data privacy through Enterprise Frontier Safeguards (EFS), and more precise safety measures that reduce false positives. The models demonstrate state-of-the-art performance on benchmarks like Terminal-Bench-Science 0.1 and Terminal-Bench 4.0, and early-access partners report superior coding and scientific research capabilities. Notably, Mythos 5.1 has shown promising results in molecular design, computational analysis for planetary mapping, and optimizing deep learning models for biology. The release also details extensive safety testing, alignment improvements, and compliance with the EU AI Act's transparency requirements.

(Source：Anthropic)