I had the same question and asked Van's Aircraft. Van's stated "Any spar serial # greater than 869 is a -1 spar." The spar number is etched into wing near root as you can see in photo. The original spar has a aerobatic gross weight of 1,550 lbs and updated -1 spar has aerobatic gross weight of 1,600 lbs. You can also see "-1" listed in packing list of wing kit if that is what was provided. I received my QB kit in 2001 with the newer -1 spar.