I had to check, I didn't know the 18 SQ5 came with the regular 4 pot calipers. My wife upgraded her 2020 Q5 for a 2022 SQ5 and all the models come with the 6 pot brembos, just painted red for the Sport package.
Her Q5 brakes did surface rust just like my GTI, I don't think I ever had a car that the rotors didn't develop surface rust in my life.
If you can and have a chance, I would paint the hats on the discs. I had several Z-coated and E-coated discs develop rust.
I think I confused a lot of folks with my original post. The braking surface will rust. The coated surfaces should not.
BUT the braking surface of various rotors seems to rust to varying degrees. We have 3 vehicles...
1. 2018 SQ5 with coated stock rotors that were put on about a year ago. They do not rust except on the braking surface, and that rust is moderate, not severe.
2. 2022 Acura MDX with coated stock rotors. These rotors literally do not rust at all. Not even on the braking surface. So they are clearly made with something headed toward a stainless steel metal mixture. Less iron, more chromium (or similar).
3. 2015 GTI with the coated stock rotors that had never been replaced. These are AWFUL. as you can see from the photos, even the braking surface never came clean. Even after a significant amount of driving and braking, then never looked better than my photos. I would not buy the OE VW rotors again. They are garbage (at least they were in 2015).