Why does that seem unlikely? The difference between frontier and open weights has been much less than 12 months for a while now.

US open weights are much worse, way more than 12 months apart compared to frontier.

Frontier and open weights? Yes. Frontier and _US_ open weights? No.

I'd expect an open weights provider to suddenly get bought or go non-open if they get near Opus 5.5 anyway.

People say this about the frontier every time, and the open models catch up in a matter of months every time.

The open models catch up, the _US_ open models catch up much more slowly. Different incentives and cultures.