Anthropic's Fable 5.1 trims costs, sharpens performance, and loosens safeguards

Anthropic launches Fable 5.1 with the same $10/$50 per‑million price, but slashs cache reads to $0.25 per million and generally outperforms Fable 5 and Opus 5 at lower cost, including a notable leap on Terminal‑Bench‑Science. Safeguards are tightened less often (cyber interventions ~60% fewer; biology ~85% fewer), while new protections like a watermark detection API and Enterprise Frontier Safeguards enable zero data retention by storing data in the customer’s cloud. Fable 5.1 remains gated to certain plans or credits, and Mythos 5.1 stays restricted to trusted access; Anthropic also strengthens anti‑distillation measures and preserves overall performance gains across benchmarks.