You don't do that - you lots of small incremental refactors. I think Google also have tools to make a large refactor into a small change. (i.e. you create the

You don't do that - you lots of small incremental refactors. I think Google also have tools to make a large refactor into a small change. (i.e. you create the new API, migrate stuff to use it, deprecate the old one, migrate the rest, retire the old one).