Anthropic blocks public access to Claude Fable 5 and Mythos 5 models following US government order

Claude Fable 5 and Mythos 5 models following US government order">

The US government last night issued an unprecedented export control directive ordering Anthropic to immediately suspend all access to its top-tier Claude Fable 5 and Claude Mythos 5 models for foreign nationals, citing unspecified national security authorities. In response, Anthropic has blocked all public access to both models, globally — meaning no users around the world can access them at this time, even paying enterprise customers and Anthropic employees internally. It's a huge blow and reversal following the public release of Fable/Mythos 5 just three days prior.

Current Fable 5/Mythos 5 sessions will end in errors and new queries will be automatically routed to older, less capable models like Opus 4.8. Anthropic says in a blog post that "We believe this is a misunderstanding and are working to restore access as soon as possible," and apologizes to its customers. The sudden regulatory intervention serves as a stark warning to the enterprise sector: centralized, cloud-based frontier models exist at the absolute mercy of government oversight and vendor compliance.

Did Pliny the Liberator's public jailbreak catalyze the extraordinary USG action against Fable/Mythos 5? The government's sweeping action follows a viral jailbreak of Fable 5 published publicly on X on June 10 by the prolific jailbreaker " Pliny the Liberator," who claimed to have successfully bypassed the model's safety guardrails to extract functional instructions for cyber exploits, explosives, and chemical synthesis pathways, specifically noting the "birch reduction method" for methamphetamine. Pliny outlined a highly sophisticated, multi-agent attack that leveraged a combination of "Unicode, homoglyphs, Cyrillic," long-context reference tracking, and a technique of breaking harmful requests into innocuous, out-of-distribution tokens.

The attacker then used a previously jailbroken Opus model to piece the benign chunks back together into actionable, restricted outputs. Anthropic doesn't specify if this is the jailbreak that precipitated the government order, and in fact, notes that the information provided by the U.S. government regarding the specific jailbreak has been poorly documented, writing: "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.

Our understanding is that one potential jailbreak was shared with the government." The company argues the capabilities uncovered are "widely available" in other public models, explicitly naming rival OpenAI's GPT-5.5. Furthermore, Anthropic warns that pulling a commercial model over a non-universal jailbreak sets a regulatory standard that could "essentially halt all new model deployments for all frontier model providers". The Pentagon precedent and need for enterprise AI redundancy and diversification This sudden blackout of Anthropic's latest and greatest AI models will no doubt cause some consternation for organizations relying primarily on the Claude API — as it should, even though they still have access to other, less powerful Claude models.