Does anyone know if the AppEngine standard environment supports kotlin coroutines?

What kind support? Coroutines just compiled to byte code and do not require runtime support except stdlib/kotlinx.coroutines, both of them just JVM libararies

We're running Ktor in AppEngine Standard, which uses coroutines internally and it works without issues

Found out it supports it, was getting a weird class definition error but I think adding the experimental tag for coroutines in the gradle fixed it.

Experimental flags in Gradle used only for compiler (mostly to suppress warnings of experimental/obsolete declarations) and do not work on runtime, so I don't think that it was related to your problem with class definition