Cybersecurity vets protest ‘dangerous’ US government ban on Anthropic’s most powerful models

Anthropic said that the White House export control order may have been based on a report that there was a method to bypass — or jailbreak — Fable to unlock its powerful Mythos-level capabilities. 

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According to Katie Moussouris, one of the signatories of the open letter, the method was demonstrated by Amazon researchers in a paper that is not public but that she has reviewed. 

But Moussouris said in a blog post that the paper did not actually demonstrate a real jailbreak. Instead, she wrote, the researchers simply asked Fable to fix open source code with public and known vulnerabilities along with “deliberately planted vulnerabilities,” after the model initially refused to “review the code for security issues.”

“The behavior described in the paper cannot meaningfully be fixed, and any attempt would only weaken the model for defense,” Moussouris wrote. “Defenders need to be able to ask AI to fix the bugs in a file, explain why the fix matters, and write tests that confirm the patch works. That is not a guardrail bypass. It is the most valuable thing an AI model can do for defensive security: executing the find, fix, and test loop defenders run every day.”

Moussouris’ critique was echoed in the open letter, which also said that the group of experts believe the method in the Amazon paper “can be replicated” on OpenAI’s GPT-5.5, on Anthropic’s own publicly available Claude Opus 4.8 and Sonnet, “and even Chinese models like Kimi 2.7.”

The letter also asked for transparently and fairly enforced regulations created by “a democratic rule-making process” that are based on scientific research done by industry and academic experts, and “used only to the minimal extent necessary to ensure the safety of the American public.”