Anthropic releases Claude Fable 5: Mythos model with built-in guardrails

Anthropic has released Claude Fable 5, a version of its Mythos-class model adjusted with safety controls. Fable 5 uses the same underlying model as Mythos but adds safeguards that block responses in specific high-risk areas of cybersecurity and biology. When a prompt veers into those areas, the model falls back to Claude Opus 4.8, which carries its own restrictions.

Mythos was introduced as a model capable of finding vulnerabilities in code and has been limited to Project Glasswing partners, including Amazon Web Services, Anthropic, Apple, Broadcom, Cisco, CrowdStrike, Google, JPMorganChase, the Linux Foundation, Microsoft, Nvidia, and Palo Alto Networks.

Anthropic is also launching Claude Mythos 5 for users with Mythos Preview access and says it plans to expand access over time through a trusted-access program. Pricing for Fable 5 and Mythos 5 is set at $10 per million input tokens and $50 per million output tokens, roughly twice the price of Claude Opus 4.8.

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