Note that we're not ever spinning up a Python interpreter to run your code, or monitoring an existing running Python process. So we do need some kind of metadat

Note that we're not ever spinning up a Python interpreter to run your code, or monitoring an existing running Python process. So we do need some kind of metadata. But yes, if you have a Python version specified in pyproject.toml, we respect that, and if you have a virtualenv, we can see the Python version that was used to create that. And that's what we use to type-check your code. The default being discussed here is what we fall back on if that project metadata isn't available.