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Anthropic Releases Claude Fable 5 with Jailbreak Resistance

Anthropic Releases Claude Fable 5 with Jailbreak Resistance

ATLAS OWASP HIGH Significant risk · Prioritise patching ▲ 7.2 SecurityWeek

Anthropic's release of Claude Fable 5, a Mythos-class frontier model, has prompted significant industry debate over its dual-use offensive capabilities in cybersecurity and biology. The model includes a capability fallback mechanism — downgrading to Claude Opus 4.8 in high-risk domains — alongside extensive jailbreak-resistance red-teaming. Security professionals are warning that frontier AI capability investment directly accelerates attacker tooling for machine-speed, AI-orchestrated 'hyperattacks' that outpace human defenders.

Claude Fable 5 Jailbreak Attacks Bypass Fallback Defense

Claude Fable 5 Jailbreak Attacks Bypass Fallback Defense

ATLAS OWASP MEDIUM Moderate risk · Monitor closely ▲ 7.2 SecurityWeek

Anthropic has released Claude Fable 5, a high-capability 'Mythos-class' model that automatically falls back to a less capable model (Claude Opus 4.8) when queries touch sensitive domains like cybersecurity and biology. The company conducted over 1,000 hours of external red-teaming with no universal jailbreaks discovered, though it openly acknowledges financially motivated adversaries will attempt to circumvent these controls. Trusted cybersecurity partners under Project Glasswing receive elevated access to the full Mythos 5 capabilities, raising questions about insider risk and tiered trust model security.

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