Anthropic Returns Claude Fable 5 to Service and Proposes a Shared Jailbreak-Severity Scale

Anthropic redeployed Claude Fable 5 worldwide on July 1 after a 19-day suspension, according to its announcement. The suspension followed a US Commerce Department export-control order that pulled Fable 5 and the larger Mythos 5 offline from June 12, issued after Amazon researchers found a jailbreak that induced Fable 5 to flag software vulnerabilities and, in one case, write exploit-demonstration code, as reported at the time.

Alongside the return, Anthropic published a draft Cyber Jailbreak Severity (CJS) framework developed with Amazon, Microsoft, Google, and other members of its Project Glasswing coalition. The scale rates a jailbreak from CJS-0 (informational) to CJS-4 (critical) across four axes: capability gain over tools an attacker already has, breadth across offensive tasks, ease of weaponization, and discoverability. The bands are exponential, so each level is meant to represent several times the real-world risk of the one below.

The episode is notable on two fronts. It is the first widely reported case of an export-control mechanism used to pull a commercial model from global service over a security flaw, and it shows the three largest cloud providers coordinating on a severity standard that could become a de facto baseline. Anthropic also relaunched with a hardened classifier and a HackerOne bug bounty, moving remediation into public view.