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Mythos 5

Illustration of butterflies breaking through bent prison bars, symbolizing the lifted restrictions on Fable 5 and Mythos 5.

U.S. Government Lifts Restrictions On Anthropic’s Fable 5 And Mythos 5

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Fable 5 is now generally available, while Mythos 5 continues its approved rollout through Anthropic’s Glasswing program after the government ended restrictions on both frontier AI models.

Anthropic resumed access to its Fable 5 and Mythos 5 frontier AI models after the U.S. government lifted restrictions that temporarily halted their release due to national security concerns.

The announcement marks the end of an unusual government intervention that interrupted the launch of Anthropic’s most advanced AI models. Under the updated arrangement, Fable 5 is now generally available, while Mythos 5 continues its approved deployment through Anthropic’s Glasswing program for select enterprise partners, consistent with the authorization the company received on June 26.

The restrictions began on June 12, just three days after Anthropic introduced Fable 5 and Claude Mythos 5, when the U.S. government directed the company to suspend public access while additional national security evaluations were conducted. The restrictions marked an unprecedented government intervention in the release of frontier AI models.

On June 26, the government approved the limited return of Mythos 5 through Anthropic’s Glasswing program, allowing a select group of enterprise organizations to begin using the model. The latest announcement completes the process by restoring access to Fable 5 and formally ending the temporary restrictions on both models.

In an X post announcing the decision, U.S. Commerce Secretary Howard Lutnick confirmed that the government lifted the remaining restrictions following its review. Anthropic separately announced that Fable 5 is now publicly available and reaffirmed that Mythos 5 will continue to be offered through Glasswing, the company’s controlled deployment program for advanced frontier models.

Anthropic said the company appreciated its collaboration with the U.S. government throughout the review process and reiterated its commitment to the responsible deployment of increasingly capable AI systems.

Vintage butterfly S illustration on a laptop screen amid a blue digital network, representing Anthropic Mythos 5 limited release.

U.S. Allows Limited Release Of Anthropic’s Mythos 5

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Commerce Secretary Howard Lutnick authorized limited access to Anthropic’s cybersecurity-focused Mythos 5 model for approved organizations while broader restrictions remain in place.

The U.S. Commerce Department approved the limited release of Anthropic’s Mythos 5 AI model to select organizations, while continuing to restrict access to its consumer-focused Fable 5 model.

According to a letter from Commerce Secretary Howard Lutnick reviewed by Reuters, the authorization allows Anthropic to give access to Mythos 5 to a defined group of trusted U.S. organizations following the government’s earlier suspension of both models. Axios, which also reviewed the letter, reported the decision followed what the department described as “significant progress” by Anthropic in implementing appropriate safeguards.

According to Reuters and Axios, the letter includes five key provisions:

  • Limited access to Mythos 5 is restored. Anthropic may now provide the model to approved trusted organizations under the revised authorization.
  • Access is limited to approved organizations. Reuters reported that more than 100 organizations, including many Fortune 500 companies and critical infrastructure partners, are eligible under the authorization.
  • Foreign-national employees may use the model. Employees of approved organizations may access Mythos 5 without requiring additional export licensing, according to Reuters.
  • Commerce retains the authority to modify the decision. Reuters and Axios reported that the department reserved the right to revise or withdraw the authorization if circumstances change.

Earlier this month, the Commerce Department directed Anthropic to suspend access to Mythos 5 and Fable 5 after national security concerns emerged following a reported jailbreak involving the models.

The White House decision follows another recent example of government involvement in frontier AI deployments. On the same day, OpenAI announced it would limit the release of its new GPT-5.6 Sol model at the request of the U.S. government.

Anthropic said it is working to restore access to Mythos 5 for approved organizations while continuing discussions with the U.S. government regarding the broader availability of its frontier AI models.

Butterfly and moth specimens forming the numeral five under a cybersecurity grid, for freefable.org's letter to lift the Fable and Mythos ban.

130+ Technology Leaders Demand U.S. Lift Fable and Mythos Suspension

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freefable.org, formed in response to the June 12 directive, published an open letter arguing the ban disarms defenders without restricting what attackers can already use in other models.

 

More than 130 information security executives, researchers, and academics published an open letter on June 14, formally calling on the U.S. government to lift the Fable and Mythos suspension imposed two days earlier.

The letter was published at freefable.org, an organization formed specifically in response to the directive that prompted Anthropic to cut access for all users on June 12. It is addressed to Commerce Secretary Howard Lutnick and National Cyber Director Sean Cairncross. Notable signers include Bruce Schneier, one of the most widely cited voices in computer security, affiliated with Harvard University and the University of Toronto; Philip Zimmermann, creator of the PGP encryption standard; and Vinh Nguyen, former Chief Responsible AI Officer at the National Security Agency. The group spans CISOs, CEOs, security researchers, and academic faculty across the U.S. and allied countries.

They argue that Mythos-class models can find software flaws and generate exploits, but are not unique in this. The same capabilities exist in GPT-5.5, Opus, Sonnet, and Chinese open models, including Kimi 2.7. The signers contend that removing the best American tools from defenders without restricting what attackers can already access elsewhere weakens defense without limiting offense. The letter also challenges the jailbreak evidence the government cited to justify the directive. The signers say what the jailbreak unlocks in Fable is already freely available in other models without bypassing any safeguards. Fable’s jailbreak, they argue, does not give attackers capabilities they could not already access elsewhere. Anthropic is working to close the specific vulnerability.

If the government does pursue AI risk regulation, the letter says it should be grounded in scientific consensus developed with industry and academic input, created through democratic rule-making, enforced transparently with time to remediate, and applied only as far as necessary to protect public safety.

The letter remains open for additional signatures at freefable.org. The government has not publicly responded.

Butterfly and moth specimens forming the numeral five, cut by a red and white barrier with a stop sign, representing the suspension of Fable 5 and Mythos 5 access.

Anthropic Shuts Down Fable 5 and Mythos 5 After US Government Security Directive

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Unable to verify which customers are foreign nationals, Anthropic cut access for everyone.

 

On June 12, the US government ordered Anthropic to suspend access to Fable 5 and Mythos 5 for foreign nationals, citing national security concerns. To comply, Anthropic shut down access for all users, saying it has no mechanism to verify customer nationality.

The government says it has become aware of a jailbreak for Fable 5. Anthropic disputes the severity, calling it a non-universal jailbreak that works only in limited situations and only enables what other AI models already do freely.

Anthropic complied, but is pushing back. What the government shared, Anthropic says, constitutes a narrow, non-universal technique: one that works only under specific circumstances, not one that broadly defeats the model’s safeguards.

Anthropic said at the time of launch that no AI model can be made completely jailbreak-proof. Their stated strategy was to minimize the damage any jailbreak can cause, make them difficult to execute, and catch them quickly. The 30-day data retention requirement on Mythos-class models is part of that: it lets Anthropic review usage and shut down jailbreaks as they appear.

“If this standard was applied across the industry,” Anthropic said, “we believe it would essentially halt all new model deployments for all frontier model providers.”

 

Background

Mythos 5 and Fable 5 launched three days before the directive. Mythos 5 is available exclusively to vetted large tech companies, US and allied government organizations, and cybersecurity firms through Project Glasswing, Anthropic’s program for organizations that use AI to hunt for software vulnerabilities before attackers find them. 

Fable 5 is the consumer version of the same underlying model, with filters that detect hacking-related requests and route them to a less capable model, Opus 4.8, rather than allowing Fable 5 to respond.

Glasswing launched in April 2026 with Claude Mythos Preview, the predecessor to Mythos 5. Partners in the project identified more than 10,000 vulnerabilities using Mythos Preview, including bugs that conventional security tools had missed.

The relationship between Anthropic and the US government is strained. The US government takes an active role in vetting which organizations can access Mythos 5 through Glasswing. This cooperation exists despite an ongoing lawsuit where Anthropic sued the Department of War after the DoW designated Anthropic a supply chain risk earlier this year.

 

Anthropic says it believes the suspension is a misunderstanding and is working to restore access as soon as possible.