It is, however, a commit object per change because of how jj tracks the evolution of commits. Those intermediate/ephemeral commits will not be able to be GC'd from git object storage until they are either abandoned in jj or are removed from the jj op log. The latter of which AFAIK does not happen automatically, not even on a time/age basis.

I am an extremely fervent believer in jj and use it exclusively since December '24, but I think it's useful to be accurate as possible for these kinds of trade offs. I don't use watchman snapshots specifically because of this downside.