It was completely clean-sheet and the first plane to fly with the new Geared Turbo Fan engines from Pratt. It is very, very efficient, and very, very quiet. It will have much better operating economics than the 737Max or A320neo as well. Time will tell if it ever gets any traction in the market though...so far there are <200 firm orders despite the economic advantages. I expect a rash of new orders after it gets some more hours behind it and enough confidence that it will deliver in a year or so vs. the years of delays typical of Boeing and Airbus.