Good news this morning for those of you who have the HTC One A9 on Sprint. Android Nougat is rolling out to you starting today. The software update from the carrier is build 2.18.651.2 and it brings Android Nougat 7.0 to your phone along with the January Android Security update. With it, you get all the goodness that is Nougat including multi-window support, improved data saver and other features.
The OTA update should be hitting devices soon but you can always manually check for it by going to Settings>System Updates>HTC Software Updates on your phone. As these things tend to go, it will take a few days before everyone sees the update so patience is required.