Your best bet for now is to keep track of the index of the last item retrieved in the application layer. In other words, when you call liststreamkeyitems, pass your internal record of this value in the start parameter, and then increment your internal record based on the number of items you get back. That way next time you'll only be retrieving new items. Note that for this to work reliably, you should use local-ordering=true in this API, in which case different nodes might get differently ordered results.