Anthropic Blocks Public Access to Claude Fable 5 and Mythos 5 After US Government Order

The U.S. government has issued an export control directive to Anthropic, mandating the immediate suspension of all access to its top-tier Claude Fable 5 and Claude Mythos 5 models for foreign nationals. The directive cites unspecified national security authorities as the basis for the order.

In response, Anthropic has blocked all public access to both models globally. This means users worldwide, including paying enterprise customers and Anthropic employees, cannot currently access these models. The action comes only three days after Fable 5 and Mythos 5 were publicly released. Current sessions using these models will terminate with errors, and new queries will be automatically rerouted to older, less capable models such as Opus 4.8. Anthropic stated in a blog post, "We believe this is a misunderstanding and are working to restore access as soon as possible," also issuing an apology to its customers.

The government's action follows a viral jailbreak of Fable 5, published publicly on June 10 by an individual identified as "Pliny the Liberator." This individual claimed to have bypassed the model's safety guardrails to extract instructions for cyber exploits, explosives, and chemical synthesis pathways, specifically mentioning the "birch reduction method" for methamphetamine.

Pliny described a sophisticated multi-agent attack that utilized Unicode, homoglyphs, Cyrillic characters, long-context reference tracking, and a technique to break harmful requests into innocuous, out-of-distribution tokens. These benign chunks were then reassembled into actionable, restricted outputs using a previously jailbroken Opus model. Anthropic has not confirmed this as the specific jailbreak that prompted the government order, noting that the information provided by the U.S. government regarding the potential jailbreak has been poorly documented. Anthropic stated that the government has only provided verbal evidence of a "narrow, non-universal jailbreak" involving fixing software flaws in a codebase. The company argues that the capabilities uncovered are "widely available" in other public models, specifically naming OpenAI's GPT-5.5, and warned that halting a commercial model over a non-universal jailbreak could "essentially halt all new model deployments for all frontier model providers."

This regulatory intervention highlights potential operational challenges for organizations relying on single AI models or providers. In March 2026, Secretary of Defense Pete Hegseth reportedly labeled Anthropic a "supply chain risk" after the company refused to allow military use of Claude for mass domestic surveillance and lethal autonomous weapons without safety restrictions. This led to a prohibition on Anthropic's use across defense supply chains.

The incident has prompted discussions within the enterprise sector regarding AI redundancy and sovereign setups. AI founder Alex Finn suggested running local models on GPUs to mitigate regulatory volatility. Chinese open-source AI provider MiniMax also emphasized the decentralized availability of its M3 model, contrasting it with the centralized vulnerability of models like Claude. Enterprises face a trade-off between the control and data privacy of local, open-weights models and the cutting-edge capabilities of centralized, cloud-based frontier models. An active fallback architecture, designed to be model-agnostic and able to switch between providers or local models during outages or bans, is suggested as a resilient path forward.

(Source: VentureBeat)