Anthropic's Fable 5.2 and Mythos 5.2
- Anthropic documentation published November 10 revealed that framing a codebase as the model's own in a prompt caused Fable 5.2, released November 9, to merge repeated code in roughly half of small coding tasks versus fewer than one in ten without that framing.
- Hardware and physics results from the launch also gained external confirmation: Diode Computers said it built three electronic devices directly from the model's output without change orders and scored it at 69% on PCB Gym versus 25% for Fable 5, and a physicist verified Fable 5.2's completion of a black hole formation calculation physicists had left unsolved since 2003.
The release combines autonomous coding at scale, physics and mathematics results verified by domain experts, and hardware design output manufactured without revision. The prompt-ownership finding shows that documented framing techniques can materially shift the model's coding behavior.