This is not what add X#julia-0.7 does; it says that the project (or package) depends on X, and that the environment (i.e. Manifest) should track the julia-0.7 branch. Since there’s only one environment active, that does not work as a general strategy (i.e. you could work in X’s environment, but then Y’s dependency on Z#julia-0.7 will be ignored). AFAIK, there’s no way to say that a package depends on some branch of another package. However, you can still have an environment in which all the branches you want are loaded: