Yup, alumunum
Sorry, I was going on the weight of the inner pot on the Cuisinart, which I've been using in lieu of the PPCXL for the past couple of months. It's a relatively heavy gauge, which led me to think it's stainless, but when I held a magnet to it just now, there wasn't even a slight attraction, so it must be aluminum. I also got the XL out of its box and saw that It has to be aluminum as well. Makes sense, since few stainless pots and pans come with non-stick coating. Probably some difficulty in getting the coating to adhere to stainless.
However I'm not sure how much of a difference the inner pot material makes to me. To me the drawback of the PPCXL is the restrictive nature of the menu buttons. The Cuisinart is much more flexible ... for brown rice, for example, I just choose the "HIGH" setting and then input any number of minutes I want, using the suggested times in the owner's manual as a guide. With the PPCXL the rice option doesn't cook long enough, so I have to select the BEANS option instead. That annoys me.
Under normal use, the inner pot in any of these appliances should never get to the temperature that would degrade a non-stick coating. On the stove top, yes, it's possible. If you put an empty pot on the burner, set it to high, and walk away for 30 minutes. So don't do that.
And no, I'm not particularly happy with the PPCXL. Which is why I've been using the Cuisinart instead. Smaller (6qt) but I find it easier to use.
If I had to do it over again, I would not have purchased the PPCXL. But one can't know such a gimmick's drawbacks until one tries it. I could probably still return it to Costco, with some grumbling. I doubt I'd get an Instant Pot as its replacement, however. Don't need another gimmick, no matter how high quality part of it is.
And to be honest, we have a number of members who look down upon any of these electric pressure cookers, because in their opinions they don't achieve a high enough pressure and temp to do true pressure cooking. They have a point. Which is why I have collection of range-top pressure cookers should I need to get something sterilized or pressure canned.