Sprint has started pushing out the Android Nougat v7.0 update to it's HTC One M9 units. This was officially confirmed by the HTC - source link provided below - that the update is now on it's way to the Sprint HTC One M9. Arriving in with software version 4.27.651.4, the update also brings android security patch for the month of February 2017.
This might be the last major update that this device will receive, it will bump the Android Marshmallow to the Nougat.
As usual it's an OTA update so will take time to reach every unit. Those who are impatient can manually check for the update by heading to Setting's menu of their device. It's a large update so make sure you are connected to decent internet connection and your device is charged up to 50 percent.