Anthropic kills Fable 5 and Mythos 5 after U.S. government security order

Late Friday evening, Anthropic disabled access to Claude Fable 5 and Mythos 5 for every single one of its customers. Not just some users. Not just certain countries. Everyone.

The company received an export control directive from the U.S. government at 5:21 PM ET, citing "national security authorities," and instructing Anthropic to suspend all access to the models by any foreign national, whether inside or outside the United States, including foreign-national Anthropic employees.

Because filtering by nationality across a global customer base isn't practically enforceable, Anthropic said it had to disable the models entirely for all customers to comply.

The directive came from Commerce Secretary Howard Lutnick. The Commerce Department did not immediately reply to a request for comment.

What are Fable 5 and Mythos 5?

Fable 5 and Mythos 5 were announced just days before the suspension, and Anthropic had touted them as state-of-the-art across several industry benchmarks. The two models share the same underlying architecture, but Fable adds a layer of safeguards. Fable blocks or redirects sensitive queries around cybersecurity, biology, and chemistry, while Mythos 5 in its unrestricted form was only available to vetted government cyber defenders and life sciences partners.

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Fable 5 marked the first time Anthropic released such an advanced model to the public, made possible by new safeguards the company had spent months developing.

What exactly spooked the government?

The government's letter didn't provide specific details of its national security concern. Anthropic says its understanding is that officials became aware of a method of bypassing, or "jailbreaking," Fable 5, and that one potential jailbreak was shared with the government.

But Anthropic is pushing back on the reasoning. The company reviewed the report it believes forms the basis of the government's directive and says the level of capability demonstrated there is widely available from other models, including OpenAI's GPT-5.5, and is used daily by security defenders.

In the weeks before Fable launched, Anthropic worked with the U.S. government, the UK AI Safety Institute, multiple private third-party organizations, and internal teams to red-team Fable's safeguards for thousands of hours. Those tests showed Fable's protections were substantially more effective than any previously deployed model, and no testers were able to find a universal jailbreak.

The company says it believes the directive is a misunderstanding and is actively working to restore access.

Why this matters

This appears to be the first time a leading AI company has taken a publicly deployed model offline due to direct intervention from the federal government. That's not a small thing. Regardless of where you land on the security question, the precedent is significant.

All other Anthropic models, including Claude Opus 4.8, remain unaffected. For developers on the platform, new sessions will fall back to the user's default model or Opus 4.8, existing Fable 5 sessions will end with an error, and Anthropic has told integrators to migrate to other models.

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