E.K. Johnston’s novel Ahsoka has made it to #1 on the New York Times’ Bestsellers list for Young Adult hardcovers, per Lucasfilm’s Jennifer Heddle. The October 30th list isn’t online yet, but Ashley Eckstein has a shot of the print version.
This is far from the first Star Wars novel to make it to #1 on an NYT list (several novelizations and Heir to the Empire) but I believe it is the first YA to make the list at all. (Of course, keep in mind that the Star Wars YA novel is a very recent phenomenon, unlike the adult and middle-grade lines.)