Anthropic’s Fable 5 is back worldwide after a two-week government ban over a jailbreak

After a two-week ban, the US government is letting Anthropic ship Fable 5 globally again. Amazon researchers had found a jailbreak, but Anthropic says even much smaller models like Claude Haiku 4.5 could pull off the same exploit.

Pro, Max, Team, and select Enterprise plans include the model through July 7 at up to 50 percent of weekly usage limits. After that, it’ll be billed through usage credits. Access on AWS, Google Cloud, and Microsoft Foundry will be restored “as quickly as possible.” Mythos 5, the less restricted version of the same base model, remains limited to a group of US organizations that got government approval on June 26. Anthropic says it’s still working with the government to expand access to more partners in the so-called Glasswing program. Whether the EU will join remains unclear.Ad Anthropic confirms that the ban stemmed from a security finding by Amazon researchers. They had found a way to bypass Fable 5’s safety guardrails. The model then identified several software vulnerabilities and, in one case, produced code showing how to exploit one of them.AdDEC_D_Incontent-1 Anthropic says it’s “probably impossible” to make an AI model that can’t be jailbroken The US government and Anthropic spent two weeks investigating the vulnerability. Many less capable models could spot the same flaws Fable 5 found in the report, including Claude Opus 4.8, GPT-5.5, and Kimi K2.7. For the specific exploit demo, every model tested produced the same result, even much smaller ones like Claude Haiku 4.5. Anthropic calls it an edge case that only involved routine defensive cybersecurity work. In response, the company trained an improved safety classifier that blocks the technique from the Amazon report in more than 99 percent of cases. When a request gets blocked, users see a notification, and the request gets routed to the older Opus 4.8 model.Ad The new classifier comes with a tradeoff, though. It flags harmless requests more often during everyday coding and debugging. Users had already complained the model was too restrictive during the first Fable release. No universal jailbreak was found at the time of release.