After struggling a bit to find the right markings, I finally called our CS and confirmed they're summer tires.
The 19" nonPP stock tires are labeled "Michelin Primacy4", which as best as I can tell are an updated version of the Primacy3 tires:
Michelin Primacy 3 tires deliver excellent wet and dry handling and are the best summer tire for your luxury touring vehicle. Learn more today.
www.michelinman.com
These are stated as summer tires but good for both wet and dry conditions. The main thing I'm trying to decide is if I really shouldn't take it into a location where the temps can get to freezing, but the roads should be well plowed/salted, for a trip over a few days. I'm tempted to go for it but it seems like a risk. But also seem silly to switch out to winter tires just for that.
I went ahead and ordered some chains (which I will try out before leaving!) and keep those in the frunk as a kind of halfway insurance policy.
Interesting to me, the tread pattern of my tires looks identical to both the Primacy3 (which is rated as Summer) and the Primacy MXM4 (which is rated as All Season). So guessing the Summer vs All Season diff is down to the rubber composition, which Mike from our CS also suggested.