The ideal situation here would probably be to update any identical but not reflinked files to be reflinks. But if there is no API like you suggested then it may

The ideal situation here would probably be to update any identical but not reflinked files to be reflinks. But if there is no API like you suggested then it may not be easy. Also ideally there would be an API to do this atomically please share the storage of these files assuming they are the same) If Time Machine is tracking file contents for deduplication it would be really cool if it did this to the source files whenever it noticed that they were identical.