The 4th (current generation of the 3.6 GDI which is the third GDI generation) begin use in model year 2016 and it is the current version of the engine. It provides for increased flow and power but no changes were made for carbon concerns. 2008 was the first gen GDI, the inital ATS production got the second gen GDI for early years and the the third gen for 2016 until the end of life.
A lot of the first gen GDI are still on the road and running fine without issue; the only major issue with gen 1 was the timing chain, tensioners, and guide exacerbated by a ridiculously long oil change interval that was corrected early in life.
The same basic carbon buildup strategies of the 3.6 GDI has been used in multiple displacement GDI engines by GM both in 4 valve OHC and 2 valve OHV designs. If carbon buildup were an issue, GM dealerships and independent shops would be loaded with repair work given the huge volume of these engines that have been sold since 2008. Most cars with high miles are going to have greater power loss from buildup in the cats and mufflers than from carbon on the valves, one side effect of these engines is greater exhaust particulate matter which will start to build up at very high miles in the exhaust system but again the rest of the car is probably going to be junk before it becomes significant to the performance of the car.
Cadillac was the initial user of the first 3.6 GDI engine but all of the development work was under GM Powertrain Division (since renamed Global Propulsions Division which better reflects their ICE and EV mandate). The 3.6 has served in platforms across GM and was also available in various incarnations as an OEM industrial engine via Powertrain Division.
Like other GDI engines, it will certainly have some carbon buildup on the valve stem and back of the valve but any issues (loss of power and economy) will occur with very high engine hours and it will not be sudden onset resulting in rough running and DTCs being set.
There is an industry built around selling consumers various "cures and treatments" just like there has been for other automotive concerns since the 1920s. I would be extremely careful with Youtube and other approaches to "the carbon buildup problem" because some of these magic mouse milk formula treatments can easily result in damage ranging from fouled cats through hyrdrolock with resulting bent rods and a windowed block (there is very little "squish space" in these small high compression engines so dribbling any liquid into the intake is a bad idea).
Carbon buildup is an unfortunate side effect of GDI. Some of the earliest designs (i.e. some BMW and VW engines) had horrible issues from a combination of rapid buildup and little robustness against the buildup. Later designs took the approach of both reducing the rate of formation and making engine performance robust against a small amount of buildup. Think of it like your intake air filter, it starts getting dirty from the moment you install it but it continues to function well over a long life because it is designed with the knowledge that there will be buildup.
The most important thing with GDI engines is to ALWAYS use oil formulated to avoid LSPI (low speed pre-ignition) which is a trait of almost all current automotive intended oils. Some specialty oils along with some of those designed for diesel engines don't meet this requirement and using those can definitely cause issues.
There are a lot of things that can go wrong with our cars but carbon buildup isn't one I would lose sleep over. One of the prime reasons I bought my first GDI Cadillac (a 2008 CTS) was because of the carbon buildup issues experienced by BMW along with the woefully undersized cooling system for the BMW 335i I was inches away from purchasing. It was a beautiful car that performed better than the CTS but I made the right choice back in 2008
Rodger
