Why Anthropic Temporarily Suspended Fable 5 and Mythos 5

RÉSUMÉ

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In a June 2026 video, Matthew Berman discusses Anthropic’s suspension of Fable 5 and Mythos 5 after a US government directive and argues that jailbreaks and cyber capabilities are industry-wide issues. Anthropic subsequently said export controls were lifted and access was restored, with Mythos availability still limited to selected partners.

1A claimed jailbreakBerman cites a post claiming a jailbreak soon after Fable 5 launched and questions the implications of shutting down a model on which customers depend.
2Anthropic’s accountAnthropic said the government had not specified its concern and that the technique it reviewed found a few previously known, relatively minor vulnerabilities.
3Cyber capability and comparisonBerman worries most about the discovery of unknown software vulnerabilities, but argues competing models may have similar capabilities.

À retenir

Anthropic said a June 12 directive required it to restrict foreign-national access, so it temporarily disabled both models for all customers.
Anthropic described the reported bypass as narrow and said its demonstration involved known vulnerabilities; Berman argues safeguards cannot eliminate every jailbreak.
Berman questions why similar cyber capabilities in other models did not receive the same treatment.
Anthropic later announced that the export controls had been lifted and access restored.

ThèmesAnthropic Cybersecurity AI Regulation Red Teaming

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A jailbreak and a shutdown

Berman points to an alleged early Fable 5 jailbreak and the disruption caused by taking models offline. Anthropic said the government’s directive led it to suspend both models.

Pliny the Liberator posted a claimed Fable 5 jailbreak within hours of release. I see such attempts as a recurring feature of new model launches, so the decision to shut the model down is striking, especially for companies that have come to rely on it. A claim of a jailbreak, however, does not establish a universal bypass or explain which report triggered the directive.

What Anthropic said

He reads the company’s description of the demonstration and its limits. He argues that jailbreak risk can be reduced but not entirely eliminated.

DIAPOSITIVE 1 / 1Anthropic describes the directiveThe company’s statement distinguishes the foreign-national restriction from its resulting suspension for all users and describes the reported demonstration.

Anthropic said the government believed it had learned of a method of bypassing Fable 5. The company said it reviewed a demonstration involving a small number of previously known, relatively simple vulnerabilities that other publicly available models could also identify without a bypass. Its June 12 statement said the government’s letter had not specified the national security concern. [Anthropic’s statement](https://www.anthropic.com/news/fable-mythos-access) described the directive as restricting foreign-national access, which prompted it to suspend both Fable and Mythos for all customers.

My view is that safeguards can minimize jailbreaks but cannot guarantee their complete prevention. I also argue that sensitive topics can sometimes be elicited from models, though capability and risk depend on the particular model, prompt and context; a general claim about every model should not be treated as proof of a specific bypass.

Cyber risks across the industry

Berman distinguishes routine information from the risk of discovering unknown software flaws. He questions the unequal treatment of models he considers comparable.

The more serious cyber risk, in my view, is a model finding software vulnerabilities that nobody else knows about. I question whether Fable and Mythos are sufficiently ahead of GPT-5.5 in that respect to justify treating them differently. That comparison is my assessment, not a comprehensive independent evaluation of the models.

I think Anthropic’s own warnings about dangerous cyber capabilities now shape the scrutiny it faces, while OpenAI continues to offer a model I regard as nearly as capable. My prediction that future models will be stronger and susceptible to jailbreaks is speculation. In a later [June 30 update](https://www.anthropic.com/news/redeploying-fable-5), Anthropic said the export controls were lifted and Fable access would resume globally on July 1; Mythos access was restored to a limited set of organizations while the company sought to expand it.