I'm noticing significant differences already.

Code seems to work on the first try more often for me too.

Perhaps my favorite change so far is the difference of verbosity. Some of the responses I am receiving when asking trivial questions are now are merely a handful of sentences instead of a dissertation. However, dissertation mode comes back when appropriate, which is also nice.

Edit: Slightly tangential, but I forgot to ask, do any of you all have access to the $200/month plan? If so, how does that model compare to GPT-5?