Probably. Cython compiles a C-style superset of Python into C. Then a C compiler compiles that to a Python-importable DLL/.so. So, the overhead to call a C function is no more than declaring its types (programmer person overhead) and then, in the generated C, the native C-linkage function can be called like any other. Now, just one C function calling another from another translation unit (i.e. object file or shared lib) can be "high" overhead (nothing like Py FFI), but you may also be able to eliminate that with modern compilers with link-time-optimization with some build environment care.