Last week, the company released to the public its much-anticipated Claude Fable 5 model (and its restricted version Claude Mythos 5, which is still being tested with trusted partners). Anthropic said in a blog post announcing the action that officials cited national security concerns with the new models, while offering few specific details.
The post said that the government gave the company “verbal evidence of a potential narrow, non-universal jailbreak” of the public Fable 5 model. A jailbreak is a means by which users can evade restrictions built into the code to unlock prohibited functionality. Anthropic downplayed the significance of the attack, and said other major models, such as OpenAI’s GPT-5.5, could also be affected by the technique described.
Fears of these first Mythos-class models being misused are running high, after Anthropic warned the cybersecurity world in May that the advanced cyber capabilities of Mythos have rapidly discovered thousands of vulnerabilities in ubiquitous software, leading to the decision to restrict the full version of the model to a close group of trusted partners for testing.
This morning, Axios reported that Anthropic technical staff have flown to Washington to meet with White House officials to resolve the issue.
The Wall Street Journal is reporting that the Trump administration’s decision to take action against Anthropic was prompted by discussions that Amazon CEO Andy Jassy had with officials, including Treasury Secretary Scott Bessent. According to the report, Amazon researchers said they had been able to evade some of Fable 5’s security restrictions using specific prompts. Amazon is a major investor in Anthropic.
Anthropic is currently suing the US government to fight the Pentagon’s blacklisting of the company on national security grounds.
