US Government Blocks Access to Anthropic’s Fable 5 and Mythos 5 Over Security Concerns
Anthropic has complied with a US government order suspending access to its Fable 5 and Mythos 5 models, citing national security risks. The AI firm argues the directive is disproportionate and is working to restore service while announcing new enterprise partnerships.
The US government has issued an export control directive suspending all access to Anthropic’s Fable 5 and Mythos 5 models for any foreign national, regardless of their location. Received at 5:21pm ET, the order requires the immediate cessation of access for all customers to ensure compliance with national security authorities. Anthropic has abruptly disabled these specific models for all users, while confirming that access to its other AI models remains unaffected.
The directive cites national security concerns regarding a potential method of bypassing, or “jailbreaking,” the Fable 5 architecture. According to Anthropic, the government provided verbal evidence of a narrow, non-universal jailbreak technique. This method essentially involves asking the model to read a specific codebase and fix software flaws. The company states that its internal review found the vulnerabilities identified in the government’s demonstration to be minor and previously known.
Anthropic has expressed strong disagreement with the regulatory action, arguing that the identified capabilities are not unique to its technology. The firm noted that other publicly available models, including OpenAI’s GPT-5.5, can discover these same vulnerabilities without requiring a bypass. Anthropic emphasised that such capabilities are commonly used by security defenders to keep systems safe, and that the government’s letter did not provide specific technical details to substantiate the broader security claim.
The company warned that applying this standard across the industry could effectively halt all new model deployments for frontier providers. Anthropic stated that recalling a commercial model deployed to hundreds of millions of people based on a narrow potential jailbreak is disproportionate. The firm reiterated its position that regulatory processes for blocking AI models should be transparent, fair, clear, and grounded in technical facts, asserting that this action does not adhere to those principles.
Despite the regulatory disruption, Anthropic moved to highlight its broader commercial momentum. The firm announced a partnership with Tata Consultancy Services (TCS) to provide Claude to 50,000 employees across 56 countries and to build Claude-powered products for regulated industries. Additionally, Anthropic confirmed a multi-year global alliance with DXC Technology. The company apologised for the service disruption and stated it is working to restore access to Fable 5 and Mythos 5 as soon as possible.
