GoKawiilEver since Anthropic first made the earth-shaking disclosure of its incredibly capable Claude Mythos AI model back in April and the steps it was taking toward a safe release of that product, the AI public has been waiting with bated breath to get its hands on its capabilities to give them a spin. Now, with today's release of Claude Fable 5, Anthropic says it finally has a model of this class that's "safe for general use." Anthropic is also releasing the unrestricted Mythos 5 model to members of its Project Glasswing program for use in sensitive cybersecurity and biology contexts.
As with every new cutting-edge model from frontier labs, Anthropic has a selection of benchmarks of Fable 5's performance across a range of widely accepted tests that highlight its state-of-the-art-ness, but those numbers aren't as interesting as the specific use cases that the company highlights for this level of capability.
For example, the company highlights how Stripe was reportedly able to perform the migration of a 50-million-line Ruby codebase in a single day that would have otherwise required two months of team effort had it been performed by hand. That sort of task compression on a job of such massive scope illustrates how Fable 5 and Mythos 5 "can work autonomously for longer than any previous Claude models," in addition to their high overall level of capability.
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For vision tasks, Anthropic simply says that Fable 5 is "the new state-of-the-art model." Among other accomplishments, the company says it was able to play through Pokemon FireRed in its entirety using only a "minimal, vision-only harness." Past models apparently struggled to complete this task even with the ability to seek outside help via tool-calling.
Wharton School professor and AI blogger Ethan Mollick also has vivid examples of what Fable can do. Among other tasks, he describes how he gave Fable a 19-page spec document for the development of a categorization and analysis tool for unstructured survey answers. He describes how the model worked for "nine and a half hours" to generate an "extremely sophisticated" tool that "researchers have needed for years but was never profitable to create."
In order to keep Mythos-level capabilities out of the hands of malicious actors, Anthropic says it will be redirecting queries on certain topics, namely "cybersecurity, biology and chemistry, or distillation," to the last-gen Claude Opus 4.8 instead. The company says that users will be informed whenever this redirection occurs, and that it should trigger in "less than 5%" of interactions with the model.
Mollick, however, says these limitations trip "at the faintest hint of a security problem," suggesting that even the well-intentioned won't be able to use Fable 5 to bolster the security of their code bases.
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