Anthropic could serve Opus 4.5 from a year ago under opus:latest and most heavy users would probably have no idea. Some of them would probably even prefer it.

Yes, I do use them, quite heavily. The only difference at this point is in benchmarks that can't be trusted (see: artificial analysis on Astra), or in the way models communicate.

Most gains are now from RL, which for some reason is hyperfocused on improving cyber capabilities, and harnesses. Raw intelligence gains of base models is absolutely slowing down.