It's not true, in that sense. Commits in jj are basically the same as commits in git as far as mutability is concerned. But in jj you normally work with changes, rather than commits, and open changes are mutable (by altering which immutable commit they point to in the backing store). And there is effectively an append-only audit trail of these alterations (which is what makes `jj undo`/`jj redo` simple).

Some comments here are confusing the issue by saying ‘commit’ when they mean ‘change’ in the jj sense.

Re the grandparent comment, `jj describe` provides a change description, analogous to `git commit --amend --edit` in git terms.