Lab folks keep cards close to their chests here, but it's likely Mythos was an earlier teacher model for Opus that got additional cybersec post-training. Whether they have a bigger tier than that is hard to say, labs have been cautiously scaling parameters since the failure of GPT4.1. They 100% have a bigger/better model they haven't released, but that's probably more down to it not being done cooking yet. Once it's done, the single larger model lets them drop new Opus and Mythos iterations in rapid succession.
Googlers have hinted that Gemini 3 came in at 10T, which seems hard to operationalize, Google's flash and pro releases are staggered in a way that doesn't make sense if flash is a pro distill, and there are enough cases where Gemini flash outperforms pro on the same task that I think it's unlikely it's just being distilled from an "in progress" version of pro.