I'm one of the authors. The concepts are different, we do have a concept called "tags" (not ready yet) which is more efficient than shallow clones, in the sense

I'm one of the authors. The concepts are different, we do have a concept called "tags" (not ready yet) which is more efficient than shallow clones, in the sense that you can make patches (commits) on top of a shallow clone without any down side (unlike in Git, where shallow repositories can become slower). You can also do partial clones in Pijul: since patches commute, the patches you produce on top of a partial clone can be pushed to the full repository in the exact same way.