Yeah, unused just tucked up there and glued.
The dealer I got my truck from had an LT on the floor that they had all kinds of mods on. I noticed it also had the auto dim mirror. So I was talking to one of the sales guys and he kept trying to tell me to go check out the gm accessories page (which I had already done, and the mirror wasn’t there). So I went online to try and do a build of an lt, and couldn’t even find it as an option. I was really confused because I saw it on that lt on the showroom floor.
So I figured that they wouldn’t have went completely out the their way to add the mirror and that the harness must have just been up there and when they were doing the other mods they just added it. So sure enough, there it was when I looked. I’m honestly not even sure if that mirror is ever even a factory option on this year, but it seems to work!