I've done some more testing, and the thread stack size could be smaller than 16MB, but definitely not as small as the value that's currently in thread_pthread.h.I prefer to have a slightly too large value here because IIRC the relation between the recursion limit and C stack usage is a heuristic. BTW. It should be possible to implement PyOS_CheckStack() on macOS. There are (undocumented) APIs in the public header files to get the stack base and size for the current thread. These APIs also work for the main thread:# ---#include <pthread.h>#include <stdio.h>int main(void){        printf("%#lx\n", (long)pthread_get_stacksize_np(pthread_self()));        printf("%p\n", pthread_get_stackaddr_np(pthread_self()));}# ---