Anthropic Shuts Down Mythos 5 and Fable 5 Models After US Commerce Department Directive

Anthropic completely shut off access to its Mythos 5 and Fable 5 models Friday night, just days after they were launched.

The move comes after Anthropic’s receipt of a US Commerce Department directive Friday evening, subjecting the new models to export controls restricting their use anywhere outside the United States. In a message posted Friday night, Anthropic said the only way for it to ensure compliance with that government order in the immediate term “is that we must abruptly disable Fable 5 and Mythos 5 for all our customers.” Access to other Anthropic models is not affected.

An Axios report cited an administration official saying that the administration is concerned by reports of a jailbreak that reportedly gets around broad classifier-based safeguards meant to block Fable 5 prompts regarding cybersecurity, chemistry, and biology. The administration reportedly requested a pause in the release of these models to gain time for the “national security apparatus” to be “hardened” against this kind of threat. That hardening could be complete “in the next few weeks,” Axios’ source suggested.

In its Friday night announcement post, Anthropic said the government has only provided it with “verbal evidence of a potential narrow, non-universal jailbreak” that involves getting Fable 5 to review a specific codebase for software flaws. The company says it has only seen evidence of this kind of jailbreak being used to find “minor” and “relatively simple” software vulnerabilities, and that other publicly available models like GPT-5.5 has similar capabilities on this score.

“We are complying with the government’s legal directive and are removing access to Fable 5 and Mythos 5 for all users,” Anthropic writes. “However, 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. If this standard was applied across the industry, we believe it would essentially halt all new model deployments for all frontier model providers.”

Earlier this month, President Trump signed an executive order urging AI model makers to submit to voluntary government security testing. That order came after an initial signing ceremony planned for last month was abruptly postponed amid reported concerns of disagreements about it within the administration.

Anthropic apologized to customers for a “disruption” that it said is the result of a “misunderstanding,” and said it will release more details about the situation in the next 24 hours.