Anthropic’s pre-IPO shares fall as US government shuts down its most powerful AI model

The government told Anthropic it had become aware of a method to bypass, or jailbreak, Fable 5. Anthropic reviewed the technique and said what it saw was narrow, not a universal jailbreak, and involved identifying a small number of previously known, minor vulnerabilities. It said other publicly available models, including OpenAI’s GPT-5.5, can find the same vulnerabilities without any bypass at all.

The company said the government has so far provided only verbal evidence of a potential narrow jailbreak, which it described as essentially asking the model to read a codebase and fix software flaws, a task defenders use every day.

It said applying this standard across the industry “would essentially halt all new model deployments for all frontier model providers.”

Anthropic built its entire brand around safety-first AI development, and it is now publicly disputing a national security directive on the grounds that the government’s evidence does not clear its own stated bar.

The company will share more details about the specific jailbreak within 24 hours.

The crypto market is now pricing the shutdown as a negative for the IPO case, and the Anthropic perp’s drop from its post-launch highs reflects that. The first question for the company’s public listing ambitions is whether the government’s order gets reversed, narrowed, or extended to other model classes once Anthropic publishes its technical rebuttal.