I would read the divergence as mostly evidence that Mythos et al, had offensive cyber capabilities as part of their RL training. I.e. they’re models specifically trained to be good at offensive cyber, rather than being general purpose models that happened to become good at offensive cyber via emergent behaviour from sheer scale.

The fact the Opus 5 seems to be as capable as Fable/Mythos on everything except cyber, and Anthropic explicitly say they removed all offensive cyber training data, I think lends further credence to the idea that Mythos was designed from day zero to excel at offensive cyber capabilities.

If that’s true, then we would expect divergence in open models of their capabilities come from distillation, no frontier class cyber capable model has seen significant public availability. Which means there simply isn’t data to distill from.

It also calls into question the entire narrative around Mythos capabilities being a complete surprise for Anthropic, and an inevitable outcome of scaling up LLMs.