The optimistic locking model, also known as the copy-modify-merge model, does not use locks to control access to revisions. With the optimistic locking model, multiple users can check out the same revision for editing without obtaining a lock. Users are not aware of potential changes to a revision from check outs by other users. The first user to commit changes to a revision checked out by multiple users creates the next sequential revision on the branch (assuming the checked out revision was the tip revision). Subsequent checkins by other users require a resync and merge of the previously committed changes into their working files before they are checked in to the repository.

Optimistic locking imposes the least overhead on individual users, but also provides little support for collaborative development, since the rest of the development team is not aware of a user's change until it is committed. Optimistic locking is recommended for projects with a small number of users, or where collaboration is not a priority.