Anthropic ships Claude Fable 5.1 and Claude Mythos 5.1

Anthropic released Claude Fable 5.1 and the invitation-only Claude Mythos 5.1 on September 1, 2026, describing them as its most capable models yet for coding, knowledge work and long-running research. Pricing holds at $10/$50 per million input/output tokens, but cache-read pricing drops 75% to $0.25 per million tokens. Fable 5.1 can now identify software vulnerabilities in source code and cuts Claude Code cybersecurity false positives by roughly 60%, while Mythos 5.1, restricted to vetted cybersecurity and life-sciences researchers, posts Anthropic's strongest cyber capability score yet while still landing in the low-risk tier of its Frontier Compliance Framework.