Do you mean ProcessPoolExecutor? Thread based pools don't involve serialization.

It would be good for ThreadPoolExecutor to have it as well, to make it easier to switch between executors, but only ProcessPoolExecutor is suffering from serialization overhead. Threads share the same memory space after all; references to data get passed directly, though you might choose to copy.copy or copy.deepcopy a root data "template" so each thread has its own unique copy that it can mutate.