It will only use whatever version is currently activated if that's compatible with the python version requirement specified in pyproject.toml. If it isn't, then

It will only use whatever version is currently activated if that's compatible with the python version requirement specified in pyproject.toml. If it isn't, then it will look for an installed python that is, and create the virtualenv using that instead. I'm not sure I completely love that behavior; it would be nice if it would default toward trying to use the minimum supported version, even if the currently active one is compatible. But I guess that wouldn't do anything that tox couldn't do better. You can also explicitly tell it what version to use for a project with a command like `poetry env 3.8`.