Anthropic pulls Fable 5 plug after Uncle Sam spots a jailbreak it calls meh 🪓

Anthropic disabled access to its Fable 5 and Mythos 5 models across all customers on June 12 after receiving a US government export control directive at 5:21 p.m. ET, citing national security authorities. The order instructed the company to suspend all access to Fable 5 and Mythos 5 by any foreign national, whether inside or outside the United States, including foreign national Anthropic employees. To ensure full compliance, Anthropic said it had to abruptly disable the models for every user, while reiterating that other models such as Opus 4.8 remain available without disruption.

According to Anthropic, the government's letter did not specify the alleged threat in detail, but the company believes authorities were responding to a potential method for bypassing, or "jailbreaking," the safeguards on Fable 5. The company said it reviewed a demonstration of the technique and characterized it as narrow rather than universal, describing it as "essentially asking the model to read a specific codebase and fix any software flaws." Anthropic also noted that other publicly available models, including OpenAI's GPT-5.5, can identify similar software flaws without any bypass at all.

Anthropic pushed back on the directive, stating that Fable 5 had been red-teamed for thousands of hours with the US government, the UK AISI, and multiple third-party teams before release, and that no tester had found a universal jailbreak. "To date, the government has only given us verbal evidence of a potential narrow, non-universal jailbreak," the company said, adding that applying this standard across the industry "would essentially halt all new model deployments for all frontier model providers." Fable 5 had launched publicly on Tuesday with built-in safeguards, while Mythos 5 had been released only to approved cybersecurity partners. Both were built on top of Mythos Preview, a general-purpose model the company had previously said found thousands of vulnerabilities in critical software.

The shutdown rippled into pre-IPO trading, with the Anthropic perpetual contract on Hyperliquid falling about 3.7% to roughly $1,627 on Saturday, down from all-time highs above $1,800 in the days following Fable 5's launch. Open interest on the contract sits near $8.6 million, a small figure relative to the SpaceX perpetual on the same platform but a meaningful signal for a company that has not yet filed for an IPO. Traders cited the suspension as a fresh uncertainty around the company's valuation and listing prospects.

Crypto markets also reacted, with Bittensor ($TAO) rising more than 16% on the day as commentators pointed to the directive as a case for decentralized AI networks that do not depend on a single US-based provider. Anthropic has not announced a timeline for restoring access to Fable 5 or Mythos 5 and said it will share more information as it becomes available.