Hey everybody, I've been playing guitar for 11 years and just purchased an 8 string guitar a week ago. Before this, I have had extensive experience with 25.5
scale length 7 string guitars, and classical guitars. My new 8 string is an Agile Interceptor with a 28 and 5/8th inch scale length. My first impression was that this guitar was super duper long. After a few practice sessions (~30 mins to 2 hours), I would experience some wrist pain. This pain is more noticeable if I spend more time playing on the low strings. I typically play the guitar seated in the classical position.

My questions are for more experienced extended range guitarists: Is this discomfort normal when adjusting to a new longer and wider guitar? What exercises can I do to alleviate this discomfort?
Seems to me like you're having issues stretching across frets on the low strings because you're hands aren't used to being there and are somewhat in shock, for lack of a better phrase.

It's going to be no surprise here - Just play slowly for a bit. You don't have to entirely quit playing to your full potential, but a few minutes every practice session just fiddling around slowly on the lower strings will help your hands get used to it and minimize stress on them from any sort of excess tension or weird bends in your joints. I had the same issue, but I also jumped straight to 8 strings from 6. Seeing as you have such a long scale compared to what you're used to, it might be a similar problem.
My advice would be to take it gently as suggested you do not want to make this worse. Perhaps use a capo for a week or so to ' reduce 'the scale length and see if that "cures", if not it it may be neck width or neck profile that is disagreeing with your wrist.
You didn't mention the angle of the guitar. IOW, are you playing with the guitar horizontal, or with the headstock up in the air with the neck at a 45 degree angle? I think people who learned the "classical" way to play guitar probably do a bit better with the longer scale wider neck guitars. Take a look at your hand relative to your arm next time and see if it's pretty twisted up.

I think, too, that people are beginning to appreciate the "multi-scale" or fan-fret guitars a bit more when the scales get longer and the necks get wider. The fan frets force your hand into a more natural position.