(from my understanding) YYC is now an integrated part of GMS. It's not even an option to compile an executable to include an interpreter and uncompiled code instead of compiled code. Although it's useful for debugging, interpreting on the fly is inefficient for commercial projects, as the code is read in its high-level, human-readable format, line by line while running, and "interpreted" into actual low-level instructions at runtime. That's an expensive way to process code!
Since it's not a serious professional solution for games (something typically pretty demanding of a system), YYG decided to include the compiler in their base level package when they tried to become a serious professional option. Anything else would be a big step backwards.
From my understanding, the only way to use the GMS interpreter is by using the "debug" function when testing. If you just hit "play", it complies first.
Source: my computer science education and an educated guess. (so I suppose someone on staff would need to confirm)
