Anthropic has re-deployed Claude Fable 5 and used the moment to publish something the industry has been missing: a structured framework for talking about how dangerous an AI jailbreak actually is.
Think CVE severity scores, but for AI. The Cyber Jailbreak Severity (CJS) scale runs from CJS-0 (Informational — no real uplift) to CJS-4 (Critical — domain-expert-level output that meaningfully accelerates real attacks). Anthropic is calling it an early draft and asking for feedback, but the intent is clear: standardize the language so AI developers and governments can actually communicate about these risks.
"There is no agreed-upon framework for describing a given jailbreak's severity. Such a framework would allow AI developers to speak to governments (and vice versa) in consistent terms about the risks posed by each jailbreak."
What actually changed for Fable 5
Anthropic has laid out a four-tier classifier system for cybersecurity use cases:
