another thread was just started about this with additional context on performance: https://pantsbuild.slack.com/archives/C046T6T9U/p1653336125258069 it seems like the primary thing that influenced this no longer being a symlink to an immutable venv was the desire to be able to

pip install

in the venv. but if that is going to come at this much of a performance cost, it doesn’t seem like it should be the default. “symlink to immutable venv” is pretty safe otherwise.