Anthropic completely shut down access to the Mythos 5 and Fable 5 models on Friday night, just days after launch.
The move comes after Anthropic received a U.S. Commerce Department directive on Thursday that would subject its new models to export controls that would limit its use anywhere outside the United States. In message sent on Friday nightAnthropic said the only way to immediately enforce the government’s order is to “abruptly disable Fable 5 and Mythos 5 for all our customers.” Access to other Anthropic models is not affected.
Moment Axios report Citing an administration official, he said the administration is concerned about reports of jailbreaks going around broad classifier-based safeguards designed to block Fable 5 hints on cyber security, chemistry and biology. According to information, the administration asked for a pause in the release of these models to buy time for the “national security apparatus” to “harden” against such a threat. Axios’ source suggested the tightening could be completed “in the next few weeks.”
In a post announced Friday night, Anthropic said the government had provided it with “verbal evidence of a potential narrow, non-universal jailbreak” that involved acquiring the Fable 5 only to review a specific codebase for software flaws. The company says it has only seen evidence that this type of jailbreak is being used to find “small” and “relatively simple” software vulnerabilities, and that other publicly available models such as GPT-5.5 have similar capabilities on this score.
