Anthropic Launches Claude Fable 5 with Safety Guardrails, Retains Mythos 5 for Vetters

Anthropic released Claude Fable 5, the public-facing version with built-in cyber safeguards, alongside Mythos 5, a guarded variant for vetted cyber defenders. Fable 5 routes dangerous cyber/biotech requests to Opus 4.8 and costs $10 per million input tokens and $50 per million output tokens, available via Claude API on select plans until June 22 before switching to usage credits; Mythos 5 remains restricted through a trusted-access program. The safeguards aim to block harmful tasks with some false positives, and external tests show robust defenses against jailbreaks though no system is entirely foolproof. The launch highlights a broader AI security challenge: rapid vulnerability discovery by AI, a 30-day data-retention rule to aid defense, a Cyber Verification Program for sanctioned offensive testing, and plans to broaden Mythos access and potentially fold Fable back into standard subscriptions.