Cadillac's website lists a performance cat back exhaust for 2.0 ATS
 

Cadillac's website lists a cat back performance exhaust for 2.0T coupes. You can find it under the 2017 ATS coupe build function.

The website says "see dealer for pricing". Can anyone provide a part number and can it fit 2015 ATS coupes.

My dealer told me sometimes the GM site will jump the gun on parts availability before the dealership has them for sale. He said that there was no info (part #s, price) yet, but most cases they have the item within 2-4 weeks from its debut on the corporate site. Gives you some time to save :D

I'm sure you are also aware that aftermarket exhaust systems from Magnaflow, Flowmaster, and other major suppliers are already on the market for your ride.

The problem is that 3rd party after market parts can void your warranty.

That statement holds SOME truth, but generally when it comes to cat-back systems, you're in the clear. Being a turbo mill adds another piece to the puzzle, but call your dealer to confirm liability. Also go to any aftermarket website and check their FAQ section (magnaflow.com SPECIFICALLY answers this question).