This would be by (suspected) parameter size, not benchmarked ability.

It's possible Argon/Carbon are pro sized, but given the internal rumblings and that it is based on a fresh pretrain, it makes most sense for it to be a "big" model.

Google did at one point have an "Ultra" sized model, but nothing more came of it after 1.5 Ultra.

Argon is totally in those tiers in my experience. And you actually get to use it for a few days before you run out of tokens...