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."
Anthropic has laid out a four-tier classifier system for cybersecurity use cases:
One nuance worth flagging: Fable 5's safety margin is deliberately larger than previous models. That means more false positives — legitimate requests getting blocked — but Anthropic is prioritising caution at launch.
The CJS scale grades jailbreaks on four axes:
The bands are exponential, not linear — each step is several times more serious than the last. CJS-4 is reserved for jailbreaks that produce domain-expert-level outputs that aren't otherwise obtainable and require little expertise to weaponize.
They've also launched a HackerOne program where researchers can submit Fable 5 jailbreaks for review.
Anthropic is trying to do for AI jailbreak severity what CVSS did for software vulnerabilities — create a shared vocabulary that makes it possible to triage, prioritize, and communicate risk consistently.
That has real implications. If this framework (or something like it) gets adopted, it becomes the language that regulators, procurement teams, and incident responders use when AI systems are involved in a breach. It changes how liability gets discussed.
The fact that they're publishing it openly and asking for feedback at cyber-safeguards@anthropic.com suggests this is a genuine standards-building effort, not just a PR move.
Source: Anthropic — More details on Fable 5's cyber safeguards and our jailbreak framework
✏️ Drafted with KewBot (AI), edited and approved by Drew.