Claude Fable 5.1 and Mythos 5.1

Anthropic has released Claude Fable 5.1 and Claude Mythos 5.1, described as the world's most advanced models for coding and knowledge work, with Mythos 5.1 restricted to a trusted access program for cybersecurity and life sciences use cases. Fable 5.1 delivers roughly 25% cost reduction versus its predecessor on typical token-billed workloads, rising to approximately 45% savings on highly agentic tasks, while a new Enterprise Frontier Safeguards system will give enterprise customers full data privacy without sacrificing safety controls. On key benchmarks, Fable 5.1 more than doubles Fable 5's score on agentic scientific research (52.6% vs. 24.7% on Terminal-Bench-Science) and nearly doubles performance on business workflow automation (31.4% vs. 17.1%). In scientific validation tests, Mythos 5.1 designed protein binders with affinities 10 times higher than top competition submissions and achieved a nearly 50% hit rate versus an industry norm of 10–15%, while Fable 5.1 produced a new high-resolution elevation map of Venus and accelerated computational biology models by up to 2.5 times. The release signals Anthropic's positioning of frontier models as active contributors to scientific discovery, not just productivity tools.