When I add the following to all my submodules:

tasks.withType(KotlinCompile) {
    kotlinOptions.freeCompilerArgs += ["-Xuse-experimental=kotlinx.coroutines.ExperimentalCoroutinesApi"]
}

I notice I get the following error in modules that don't use coroutines at all:

e: Experimental API marker kotlinx.coroutines.ExperimentalCoroutinesApi is unresolved. Please make sure it's present in the module dependencies

Anyone know of a fix?

Maybe you applied this compiler config to module without coroutines in dependencies? Do you use allprojects/subprojects block?

yes, that's exactly what I do

I would just apply it to particular modules or add kotlinx.coroutines dependency as simple solution

I tried to avoid setting it manually, as my teams project has so many modules (like 50+). I'm setting it based on module project dir now. I have high hopes this will work.