Anthropic completely shut down 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 US Commerce Department on Friday evening subjecting the new models to export controls, prohibiting their use anywhere outside the United States. In a message posted Friday night, Anthropic said the only way to ensure compliance with that government order in the immediate term “is for us to abruptly disable the Fable 5 and Mythos 5 for all of our customers.” Access to other anthropological models is not affected.
An Axios report cited an administration official as saying that the administration is concerned by reports of the jailbreak, which reportedly adopted extensive classifier-based security measures to block Fable 5 signals regarding cybersecurity, chemistry, and biology. The administration reportedly requested a pause on the release of these models to gain time for the “national security apparatus” to be “hardened” against such a threat. Axios’ source suggested this tightening could be completed “in the next few weeks.”
In its Friday night announcement post, Anthropic said the government had only provided it with “verbal evidence of a potential narrow, non-universal jailbreak” that included getting Fable 5 to review a specific codebase for software flaws. The company says it has only seen evidence of such jailbreaks being used to find “minor” and “relatively simple” software vulnerabilities, and that other publicly available models like GPT-5.5 have similar capabilities on this score.
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