Not unsurpisingly, he's walking far more than he ever has before. His 15 BB is on pace for over 90 BB; 50% higher than his previous career high.
People were asking "Where is the improvement going to come from now that all the big prospects are up?"
Well, MLs, at 26,27,28- the ages of Mountcastle, Hays, Mullins, Urias, Mateo- often are still getting better and adding to their games. Mullins improved his arm last year, and seems to have improved his plate discipline this year.