Anthropic’s new Fable release is cheaper, less restrictive

Anthropic released upgraded flagship models Fable 5.1 and Mythos 5.1, cutting token costs and decreasing false-positive safety blocks. Fable 5.1 is unrestricted and accessible via cloud or API; Mythos 5.1 is limited to cybersecurity and life-science partners. Both support zero-data-retention deployment and a phased rollout of Enterprise Frontier Safeguards, achieve new benchmark records on Terminal-Bench 4.0 and Humanity’s Last Exam, and the system card notes Mythos 5.1 is slightly more prone to misbehavior than Opus 5 while improving on prior Mythos versions.