I was already using orjson which is pretty much a straight 50% speed up. Calling into native doesn’t really bother me as long as I don’t have to pre compile the whole thing myself.

My experience has been that rust is significantly slower to compile than C++, by the way

It is the usual mistake to think that it does not use Python as intended (offload number crunching parts into C/C++/Fortran code eg numpy is older than many here.