The way posy does environments right now is it doesn't you can have multiple environments within a project. It's just on each command you run, it sort of knows declaratively okay these are which packages are supposed to be there,. I'll give you those packages. There isn't even a concept exactly of like, pip upgrade or pip install. Sure, you can just say that next time I invoke environment I'm going to do you different specification for which versions I want and it'll make sure that happens.