I recommend to take a look at Gerolf’s answer in Active Contract Set Service returns a Stream Arrays/List: how big can the arrays/List be per event in the stream? - #6 by gerolf. The Java APIs give you a stream of GetActiveContractsResponse. Usually those are singleton lists. I think under high load it can include more elments up to a constant batch size. I believe that batch size is 1000 from a quick look at the code but @gerolf can probably confirm that.