There isn't a stance on the build backend itself, beyond supporting the basics[0]. The spec itself however exists as the accepted successor to requirements.txt,

There isn't a stance on the build backend itself, beyond supporting the basics[0]. The spec itself however exists as the accepted successor to requirements.txt, and I think is actually implemented by all but the last tool in your list. [0] https://packaging.python.org/en/latest/specifications/pyproject-toml/ https://packaging.python.org/en/latest/specifications/pyproj...