The US government, invoking national security authorities, has issued an export control directive requiring the suspension of all access to Fable 5 and Mythos 5 for any foreign national, whether located inside or outside the United States, including foreign national employees at Anthropic. As a result, Anthropic must abruptly disable Fable 5 and Mythos 5 for all customers to ensure compliance. Access to all other Anthropic models will remain unaffected.
Anthropic received the directive on the same day at 5:21pm (ET). The letter did not specify the nature of its national security concern. Anthropic's understanding is that the government believes it has identified a method of bypassing, or "jailbreaking," Fable 5. Anthropic reviewed a demonstration of this technique being used to uncover a small number of previously known, minor vulnerabilities. These vulnerabilities appear relatively simple, and Anthropic has found that other publicly available models can discover them as well without requiring any bypass.
Anthropic's stance regarding Fable's safeguards, as detailed in the launch blog post, is as follows:
- Anthropic has implemented strong safeguards that significantly reduce the likelihood of Fable being misused for cybersecurity-related tasks (among others). In fact, the safeguards are so strict that many users have complained they are overly broad.
- In the weeks before Fable's launch, Anthropic collaborated with the US government, the UK AISI, multiple private third-party organizations, and internal teams to red-team Fable's safeguards for thousands of hours in total.
- Testing showed that Fable's safeguards are substantially more effective than those of any previously deployed model.
- No testers have yet discovered a universal jailbreak-a method that can broadly bypass the model's safeguards and unlock a wide range of cyber capabilities.
- Anthropic acknowledges that perfect jailbreak resistance is likely not currently achievable for any model provider. Every safeguard in the industry is vulnerable to non-universal jailbreaks (which can elicit some cyber information in specific circumstances), and universal jailbreaks will probably be found eventually. Anthropic stated this clearly when releasing Fable 5.
- Recognizing that perfect jailbreak resistance is not feasible today, Anthropic adopted a defense in depth strategy for Fable 5. The goal was to make jailbreaks either narrow (for non-universal jailbreaks) or very costly to produce (for universal jailbreaks), combined with thorough monitoring to quickly detect and shut down successful attacks. This is also why Anthropic requires 30-day retention of customer data with Fable-a policy change that carries real costs with customers but enables research and mitigation of jailbreaks.
- Anthropic stands by this defense in depth strategy, which reduces the risks posed by Fable to levels comparable to risks from existing models already deployed across the industry.
- Anthropic has not even received a disclosure of a concerning non-universal potential jailbreak that led to a harmful result. The potential jailbreaks disclosed so far have been either entirely benign responses or minor findings providing no Mythos-specific uplift.
To date, the government has only provided verbal evidence of a potential narrow, non-universal jailbreak, which essentially involves asking the model to read a specific codebase and fix software flaws. Anthropic understands that one potential jailbreak was shared with the government. Anthropic has reviewed a report believed to be the basis of the government's directive and validated that the level of capability shown is widely available from other models (including OpenAI's GPT-5.5) and is used daily by the defenders who keep systems safe. More details will be shared over the next 24 hours.
Anthropic is complying with the government's legal directive and is removing access to Fable 5 and Mythos 5 for all users. However, Anthropic disagrees that the discovery of a narrow potential jailbreak should warrant recalling a commercial model deployed to hundreds of millions of people. If this standard were applied industry-wide, Anthropic believes it would essentially halt all new model deployments for all frontier model providers.
As Anthropic has stated publicly, the company believes the government should have the ability to block unsafe deployments as part of a statutory process that is transparent, fair, clear, and grounded in technical facts. This action does not adhere to those principles.
Anthropic apologizes for the disruption to customers. The company believes this is a misunderstanding and is working to restore access as soon as possible.