Wasn't it that way in the previous (Lambda) design?
Kind of. We have a 2010 Acadia. Our driveway is fairly steep and in the winter you can really tell what it's doing. The default mode is FWD, the traction control/stabilitrak system will kick in the AWD when needed, and does so very quickly, but I can feel the little slippage first (my wife can't). Essentially it's an automatic version of what it sounds like has been changed to manual on the newer ones. I was surprised to read this had changed and turns me off from a new Acadia when we'll be looking in a couple years.Yes it is. I have a 2015 and AWD only.
This behavior can also seen when certain maintenance items come up. We recently had a rear wheel speed sensor go bad as well as the bearing surface that it reads off from. It was shutting down the traction control/stabilitrak/ABS, but also throwing up a message periodically saying it locked out the AWD system from engaging (not those exact words). This is all to say it's an electronic automatic system at least in the early years of AWD on the Acadias.