Anthropic's Fable 5 gets benched by the feds three days after launch 🪄

Anthropic suspended access to its Fable 5 and Mythos 5 artificial intelligence models on June 12 after the US government issued an export control directive citing national security authorities, the company said in a statement posted Friday. The directive, received at 5:21 p.m. ET, ordered Anthropic 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 compliance, Anthropic abruptly disabled the two models for every customer while leaving all other models, including Opus 4.8, unaffected.

Fable 5 had been released to the general public on Tuesday, and Mythos 5 had been released to approved cybersecurity partners, with both models built on top of Mythos Preview, a general-purpose language model that Anthropic previously said had identified thousands of vulnerabilities in critical software. Fable 5 launched with built-in safeguards designed to prevent misuse, and Mythos 5 was limited to vetted security researchers from the start.

Anthropic said the government did not provide written details about the alleged threat, but the company believes authorities are concerned about a possible "jailbreak" capable of bypassing the models' safeguards. Anthropic defended its safeguards, noting that thousands of hours of red-teaming with the US government, the UK AISI, and multiple third-party teams failed to produce a universal 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," Anthropic said, adding that other publicly available models, including OpenAI's GPT-5.5, can identify similar flaws without any bypass at all. A separate claim by an AI researcher that he had already bypassed Fable 5's guardrails has drawn attention but is unrelated to the government's stated rationale.