After being taken down by order of the US government, Fable 5 is returning to Claude’s model library. Because of the new restrictions, Fable 5 might just be Opus 4.8 in a mask.
Anthropic says Fable 5 will return to users globally on July 1. The returning version is a battened-down version of Fable 5, out of “an abundance of caution.” The user-facing model has been redesigned to more effectively handle and abort cybersecurity tasks after it was initially taken down for posing a security risk.
The company’s update states that Amazon researchers made the US government aware that it had found a method of bypassing Fable 5’s safeguards. Amazon’s testing method was to prompt the model to identify a number of software weaknesses. The testing prompt was reported as a high-security task, though Anthropic says it could have been done with any other model.
Claude Fable 5 will be available again globally tomorrow.After a series of productive conversations with the US government, we're redeploying the model with a new set of classifiers to target and block more cybersecurity tasks. In the near term, some routine tasks like coding…— Anthropic (@AnthropicAI) July 1, 2026
Anthropic claims its own testing yielded the same results with less capable models across developers, such as Opus 4.8 and GPT-5.5. Further, every model Anthropic tested produced the same results when exploiting that vulnerability, and nothing in those results revealed any unique Mythos-level capabilities.
