Anthropic launches Claude Fable 5.1 and Mythos 5.1, cutting price by 25% and targeting coding and scientific research

Claude Fable 5.1 and Claude Mythos 5.1

Anthropic released two models, Fable 5.1 and Mythos 5.1—same underlying model, different safeguards. Fable 5.1 is generally available; Mythos 5.1 is gated behind trusted access programs for cybersecurity and life sciences. Fable 5.1 beats Fable 5 across coding, knowledge work, and long-horizon tasks, while costing ~25% less on typical workloads and up to ~45% less on highly agentic work. Enterprise Frontier Safeguards (EFS) will let customers keep data in their own cloud infra, rolling out in phases from fall 2026; until then, eligible customers get zero data retention. Cybersecurity false positives dropped 60%, and the model can discover vulnerabilities but not build exploits. The post does not disclose parameter count, context window, or training details.

Why it matters: Anthropic's flagship model refresh with a dual-track release (Fable 5.1 for everyone, Mythos 5.1 gated behind trusted projects) is an industry first. Coding and long-horizon tasks beat the previous gen across the board, and bio capabilities are strong enough to require governm...