I don't know what it's using specifically under the hood, but in Street Fighter 6 Capcom recently added a new AI opponent you can fight that they say is trained on actual player ranked matches and fights more like a human opponent. You can even have it try to mimic your own playstyle if you've played enough.
It can do some odd things and its mimicry isn't perfect. But it definitely doesn't feel like the typical high difficulty CPU opponent which uses things like input reading to react faster than a real player ever could.
...it also has been seen teabagging.