Anthropic confirmed this evening that it has blocked access to Claude Fable 5 and Claude Mythos 5 for all customers, following an export control order from the US government. Here are the details.
A little context
Earlier this week, Anthropic launched Claude Mythos 5 and Claude Fable 5.
Both models are from the Claude Mythos Preview, a more advanced model aimed at security research, which has been able to detect security bugs and errors.
Access to Mythos Preview was initially limited to a small group of companies and research partners through Project Glasswing. In the following weeks, participants reported identifying and fixing many security issues with the help of the model. Mozilla alone said it has resolved several vulnerabilities as a direct result of using Mythos Preview.
When Anthropic introduced Claude Mythos 5 and Claude Fable 5 this week, the company said that the Mythos family will remain limited to Project Glasswing participants, while Fable will be available to the public.
The legend included several safeguards and restrictions intended to prevent abuse, some of which have drawn considerable criticism. Since its launch, Anthropic has been tweaking its security measures to try to strike a balance between security and usability.
Anthropic pulls Fable 5 and Mythos 5
However, earlier tonight, Axios reported that Commerce Secretary Howard Lutnick “sent a letter to Anthropic CEO Dario Amodei stating that the Mythos 5 and Fable 5 models will be subject to export controls to any destination outside the US and to all foreign nationals within the country.”
From Axios:
An administration official told Axios that the Commerce Department decided to take the action after another company said it had managed to hack Mythos, alarming the administration about national security risks.
Axios he added that the Trump administration had tried to stop Anthropic from releasing the model, but failed. The report also noted that, under the export control order, a license would be required “for the export, re-export or domestic transfer of Anthropic models.”
As a result, Anthropic announced that it has decided to disable Claude Mythos 5 and Claude Fable 5 for all customers, but stressed that access to all other models remains unaffected.
Answer from Anthropic:
The US government, citing national security authorities, has issued an export control order to stop all access to Fable 5 and Mythos 5 by any foreign person, whether inside or outside the United States, including Anthropic employees from other countries. The net effect of this order is that we have to temporarily disable Fable 5 and Mythos 5 for all our customers to ensure compliance. Access to all other Anthropic models will not be affected.
We received the order from the government today at 5:21pm (ET). The letter did not provide specific details of its national security concerns. Our understanding is that the government believes it already knows how to escape, or “jailbreaking” Myth 5. We reviewed the demonstration of this particular technique used to identify a small number of previously known, minor vulnerabilities. This vulnerability appears to be relatively simple, and we’ve found that some publicly available models are able to detect it without requiring a bypass.
The company listed the extensive safeguards it put in place when releasing Fable 5, and added that although it intends to share more information in the next 24 hours, it believes the government’s order is based on a non-universal jailbreak that includes capabilities already available in other versions, “including OpenAI’s GPT-5.5”.
Ultimately, Anthropic apologized for the inconvenience to customers, said it believed the government’s action was based on misunderstanding, and promised to work to restore access as soon as possible.
You can read Anthropic’s full statement here.
Update: Claude’s official account on X explained what users should expect as a result of tonight’s order:
For all Claude products, new sessions will run on your selected default model or Opus 4.8, and existing Fable 5 sessions will terminate with an error.
On the Claude Platform, requests to Fable 5 will also return an error. Please review your integration with other Claude models.
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