Revision numbers are stable within a given repository. The revision number for a commit is simply the index of the commit in the changelog — nothing more. Since a changeset must come after its parent in the changelog, the revision numbers give you a topological ordering of the changesets. A topological ordering is often not unique — this is why revision numbers can differ between repositories, even if they contain exactly the same commits.

Because the changelog is append-only, new commits you pull in get higher revision numbers than the existing commits. Your existing revision numbers will thus not change when you do 'hg pull' and 'hg merge'. We don't actually guarantee that revision numbers cannot change when you pull, but it's been the case until now.

In any case, the stability of the revision numbers isn't why we like them — we like them since it's often easier to type 'hg histedit 12345' than 'hg histedit c38c3fdc8b93' when you've looked up a particular changeset in your (local!) repository.

Hosting sites like Bitbucket and Kiln will wisely not show you revision numbers since the concept is meaningless when talking about more than one repository.

They can't change in a given repo unless you use history-modifying extensions. They do differ between repos. Most modern third-party tools, including Kiln, hide them by default for this reason.

Thanks for clarifying this. I haven't touched mercurial for a while.