Anthropic's Fable 5 Gets a Plot Twist: Uncle Yanks the Model After 3 Days 📖

Anthropic suspended access to its Claude Fable 5 and Claude Mythos 5 models on June 12 after receiving a US government export control directive citing national security concerns, forcing the company to disable both systems for all customers to ensure compliance. The directive, delivered at 5:21 p.m. ET, required Anthropic to suspend access for any foreign national, whether inside or outside the United States, including foreign national Anthropic employees. The company said its other models, including Opus 4.8, remain available without disruption.

The order came just days after Anthropic released Fable 5 to the general public on Tuesday, with Mythos 5 distributed only to approved cybersecurity partners. Both models were built on top of Mythos Preview, a general-purpose language model Anthropic previously said had identified thousands of vulnerabilities in critical software. In its public statement, Anthropic said the government's letter did not specify the exact national security concern, but that the company believes authorities became aware of a method to bypass, or "jailbreak," Fable 5's safeguards.

Anthropic disputed the severity of the finding, saying it reviewed a demonstration and concluded the vulnerabilities appear simple, and that other publicly available models, including OpenAI's GPT-5.5, can identify the same flaws without requiring any bypass. "To date, the government has only given us verbal evidence of a potential narrow, non-universal jailbreak, which essentially consists of asking the model to read a specific codebase and fix any software flaws," the company said, adding that thousands of hours of red-team testing with the US government, UK AISI, and third-party teams had not produced a universal jailbreak. Anthropic added: "If this standard was applied across the industry, we believe it would essentially halt all new model deployments for all frontier model providers."

The shutdown rippled into prediction markets. The Anthropic perpetual contract on Hyperliquid, a cash-settled contract tracking expected equity pricing, fell 3.7% on Saturday to about $1,627, according to data cited in reports, after trading near all-time highs above $1,800 in the days following the Fable 5 launch. Open interest on the contract sits near $8.6 million. The Bittensor ($TAO) token rose more than 16% on the news, according to one market report, amid renewed discussion of decentralized AI alternatives.

On Saturday, David Sacks, co-chair of the President's Council of Advisers on Science and Technology, wrote on X that "a highly credible, trusted partner of both Anthropic and the U.S. government who was testing Fable came forward with a jailbreak of those guardrails. The admin asked [Anthropic CEO Dario Amodei] to fix the jailbreak or de-deploy the model. Dario refused." Sacks added that Anthropic's response ran counter to its own stated positions on AI safety. Anthropic said it is working to restore access to Fable 5 and Mythos 5 as soon as possible.