Thanks for pointing this out! I'll definitely have to investigate other approaches. nanobind looks interesting but I don't need to expose complex C++ objects, I just need the 'fastest' way of calling into a C API. I guess the goto for this is CFFI?

It's the same thing - both nanobind and cffi compile the binding. The fact that nanobind let's you expose cpp doesn't prevent you from only exposing c. And IMHO nanobind is better because you don't need to learn another language to use it (ie you don't need to learn cffi's DSL).