US government forces Anthropic to disable Claude Fable 5 and Mythos 5 for all customers worldwide

The US government has ordered Anthropic to shut down global access to Fable 5 and Mythos 5, citing alleged jailbreak risks. Anthropic is complying but pushing back publicly: the vulnerabilities are minor and exist in competing models like GPT-5.5, the company says, an ironic turn after the company spent months hyping the cybersecurity risks of its own Mythos class.

The export control directive bans all access to Fable 5 and Mythos 5 by foreign nationals, whether they’re inside or outside the US. Even Anthropic’s own foreign employees are affected. To comply, Anthropic has to cut off access for all customers worldwide. All other Anthropic models remain available, according to the company’s statement. Anthropic calls the move a “misunderstanding” and says it’s working to restore access as quickly as possible. The company plans to share more details within 24 hours.Ad Government claims jailbreak risk, Anthropic disagrees According to Anthropic, the government believes it has found a method to bypass Fable 5’s safety measures. The company says it reviewed a demo of the technique and found it identifies only “a small number of previously known, minor vulnerabilities” that other publicly available models could also detect.AdDEC_D_Incontent-1 The potential jailbreak—so far only described verbally by the government—boils down to asking the model to read a specific codebase and fix software bugs. Anthropic says it reviewed the report behind the directive and concluded that the capabilities shown are “widely available from other models,” including OpenAI’s GPT-5.5. Security researchers already use these capabilities daily to protect systems. Anthropic’s own cybersecurity marketing comes back to bite it Before launch, the US government, the UK AI Safety Institute (UK AISI), private third-party organizations, and internal teams tested the model for thousands of hours combined. The safety measures are “substantially more effective than those of any previously deployed model,” Anthropic says. Users even complained they were too restrictive.Ad No tester has found a universal jailbreak, a method that could broadly bypass the model’s safety measures and unlock a wide range of cyber capabilities. But Anthropic also says that perfect jailbreak resistance isn’t possible for any model provider right now, a fact well-documented given the sheer number of attack vectors LLMs offer. Every safeguard used across the industry is vulnerable to non-universal jailbreaks that can extract some information in specific cases, Anthropic says. Knowing this, the company pursued a strategy it calls “defense in depth”: keep jailbreaks either narrowly scoped or expensive to pull off, combined with broad monitoring to quickly detect and shut down successful attacks.