Anthropic Restores Fable 5 After AI Jailbreak Triggered US Security Review

Anthropic restored global access to its Fable 5 model after temporarily restricting it in response to US government concerns that a jailbreak could enable misuse of the model’s cybersecurity capabilities. The company said Amazon researchers identified a safeguard bypass, prompting Anthropic to redeploy Fable 5 with new classifiers designed to block more cyber-related tasks while reducing false positives. Anthropic also resumed access to Mythos 5 for a limited set of US organizations and said testing found other, less capable models could identify the same vulnerabilities, suggesting the bypass did not unlock uniquely advanced offensive capability.

The episode has intensified scrutiny of how governments and AI vendors assess cyber risk from frontier models. Orion Policy Institute argued that Washington’s temporary ban and reversal exposed a broader weakness in real-world cyber-risk measurement, especially when policymakers must judge whether a model meaningfully increases offensive capability or merely replicates what existing tools can already do. Anthropic said it is now working with the US government and partners including Amazon, Microsoft, Google, and Glasswing participants to build a framework for evaluating AI jailbreak severity and determining appropriate response measures.