Are you writing a soft phone or trying to hit a specific goal? If neither of those, then I don't think it really matters which version of OPUS 3CX supports. And if you are talking about using the phone with 3CX, then answer is made very simple because you'll be using 3CX provided firmware and a 3CX template (or should be). Therefore the answer will be it supports OPUS or it doesn't. If you really want to know which variant wireshark will tell you.