It heavily depends on the task, language and experience. What I saw in my team was that low performers started being as productive as mediocre programmers, however they mostly produce slop which needs to be sent back for rework, so in the short term it's not that great. However since they can iterate faster, I have the feeling that they are learning faster so hopefully in the long run they can be somewhat productive.

The high-performers on the other hand are ripping through tasks at such a speed that they now have time to focus on quality and processes, so in the end you get a really well polished piece of software. However this is starting to change for the worse as the PMs are realizing what's happening and cramming more and more stuff in the sprints.

The amazing part is not the above though - it's that one needs not be an SME anymore. One of our customers asked us to make an Android application with some features of our product, which were not trivial to port. Even though we never did anything like that before, a small team was able to release it in a couple of months mostly bug-free. Without AI this would have taken at least half a year, or more. It is quite shocking to hear the status updates going from "we need this thing implemented and I have no idea what it even means" to "it's done and works" the next day.