AT&T subscribers who own these two handsets that were apparently stuck with Lollipop can finally move forward, as their devices receive Android 6.0. Unfortunately, there is little hope about an official Nougat update for them.
http://www.notebookcheck.net/Samsung-Galaxy-Note-Edge-and-Note-4-on-AT-T-get-Android-Marshmallow.174082.0.html