Anthropic completely closed access to its Mythos 5 and Fable 5 models on Friday night, just days after their launch.
The move comes after Anthropic received a directive from the U.S. Department of Commerce late Friday, subjecting new models to export controls that restrict their use anywhere outside the United States. In a message posted on Friday nightAnthropic said the only way to ensure compliance with that government order in the immediate term “is that we must abruptly disable Fable 5 and Mythos 5 for all of our customers.” Access to other Anthropic models is not affected.
A Axios Report quoted an administration official as saying that the administration is concerned about reports of a leak allegedly circulating extensive safeguards based on classifiers intended to block Fable 5’s hints on cybersecurity, chemistry, and biology. The administration reportedly requested a pause on the release of these models to buy time for the “national security apparatus” to “harden” against this type of threat. That tightening could be completed “in the coming weeks,” the Axios source suggested.
In its announcement post Friday night, Anthropic said the government has only provided it with “verbal evidence of a possible limited, non-universal jailbreak” that involves Fable 5 reviewing a specific codebase for software flaws. The company says it has only seen evidence that this type of jailbreak is used to find “minor” and “relatively simple” software vulnerabilities, and that other publicly available models such as GPT-5.5 have similar capabilities in this regard.
