They are not equivalent. Running a function in another process incurs the overhead of copying the data to the other process (potentially over the network). In both directions. Task.async introduces extra necessities like a linkage between the two processes, a timeout receiver, etc, and the result receiver.

Moreover, there is a context switch and it's more likely the code will run on a different core if you run it async than if you run it in the same process (which is very likely but not guaranteed) to run on the same core.

The way in which they are equivalent, is that the code that you write is identical, and the bytecode that gets run, and the existence of implicit yields is identical between the async and "sync" code.