The U.S. government on Friday ordered Anthropic to immediately shut off access to two of its most powerful AI models — Claude Fable 5 and Claude Mythos 5 — citing national security concerns. Anthropic confirmed on X that it has complied, but made clear it believes the government got this one wrong.
The directive, which Anthropic said it received on Friday at 5:21 p.m. ET, forces the company to disable both models for all users worldwide — not just the foreign nationals the government’s export control order was nominally aimed at. Access to Anthropic’s other models is not affected.
Mythos is Anthropic’s most capable AI model. The company previewed it in early April and has kept it tightly restricted ever since because of what Anthropic described as its exceptional ability to find security vulnerabilities in software. According to Anthropic, Mythos identified flaws in every major operating system and web browser it tested. Rather than release it broadly, the company launched a controlled programme called Project Glasswing, sharing it with roughly 50 vetted organizations — including Amazon, Apple, Google, Microsoft and CrowdStrike — to use for defensive cybersecurity work.
Fable 5, released just three days ago, was Anthropic’s response to the obvious commercial pressure — a version of Mythos fitted with guardrails that block responses in high-risk areas such as cybersecurity and biology, making it safe enough for general release, the company argued. It was immediately the most capable AI model available to the public, according to benchmark tests from Vals AI.
The government’s directive is framed as an export control action restricting foreign national access to the models. But in a lengthy blog post, Anthropic said its understanding is that the underlying concern is a claimed jailbreak of Fable 5. So far, the company said, the government has provided only verbal evidence of a “potential narrow, non-universal jailbreak” — one that, as Anthropic describes it, amounts to prompting the model to read a specific codebase and identify software flaws. The company added that the level of capability is already widely available in other publicly accessible models — including OpenAI’s GPT-5.5 — and is used routinely by cybersecurity professionals for defensive purposes.
Anthropic’s broader argument is that its strongest safeguards operate through independent classifier systems that function separately from the model itself, meaning that even if someone convinces Fable to keep talking past a refusal, the underlying protections against the most dangerous outputs remain in place.
None of that was enough to stop the government from acting, and Anthropic is not hiding its frustration. “We disagree that the finding of a narrow potential jailbreak should be cause for recalling a commercial model deployed to hundreds of millions of people,” the company wrote. “If this standard was applied across the industry, we believe it would essentially halt all new model deployments for all frontier model providers.”
Anthropic is widely expected to pursue an IPO this year and has staked much of its public identity on being the safety-conscious alternative to its rivals. The irony is not lost on observers that the very caution Anthropic displayed in restricting Mythos — which it promoted as a model so dangerous it could not be released publicly — has now apparently attracted exactly the kind of government scrutiny that could disrupt its business most.
OpenAI’s Sam Altman is unlikely to be displeased. In April, he told podcaster Ashlee Vance that Anthropic’s handling of Mythos amounted to “fear-based marketing.” “It is clearly incredible marketing to say, ‘We have built a bomb. We were about to drop it on your head. We will sell you a bomb shelter for $100 million,'” Altman said. Altman, whose company is also widely expected to pursue an IPO as soon as possible, did not predict a government shutdown — but he identified something that has now come back to bite Anthropic: when you spend months telling the world your AI is uniquely dangerous, the world, including the U.S. government, tends to listen.
