As pulled from PEP 512:

Since the decision has been made to work with cherry-picks instead of forward merging of branches, it would be convenient to have a bot that would generate pull requests based on cherry-picking for any pull requests that affect multiple branches. The most likely design is a bot that monitors merged pull requests with key labels applied that delineate what branches the pull request should be cherry-picked into. The bot would then generate cherry-pick pull requests for each label and remove the labels as the pull requests are created (this allows for easy detection when automatic cherry-picking failed).