Access to Fable 5 and Mythos 5 Restricted After Government Directive

On Friday evening, the government mandated that Anthropic restrict access to Fable 5 and Mythos 5 for all foreign entities, both within and outside the US, citing national security issues. This directive also applied to Anthropic’s own employees. In response, the company has entirely severed access to these models for all users.

In a statement, Anthropic acknowledged its compliance with the order but noted that the government “did not provide specific details of its national security concern.” They mentioned that any evidence of potential vulnerabilities was communicated verbally and that the issues identified were minor and also present in other models, including GPT 5.5.

The company detailed the measures it implemented to protect Fable and Mythos, which included collaborating with the US and UK governments and revising its data retention policy to monitor any attempts to misuse the models. They further stated that:
> We have not even received a disclosure of a concerning non-universal potential jailbreak that led to a harmful result. The potential jailbreaks that have been disclosed to us are either entirely benign responses or are minor findings that provide no Mythos-specific uplift.