Android 6.0.1 is pushed out to the unlocked HTC One A9

The update includes the new app permissions feature that allows users to allow or deny permission on a feature-by-feature basis. Google Now on Tap provides search results based on content that is on the screen. And With Android 6.0.1, One A9 users will receive over 200 emoji and some bug fixes. The unlocked HTC One A9 comes with a version of Android which is pretty much stock. This is why HTC promised that the phone would receive updates no later than 15 days after they are received by Nexus devices.
Once you receive notification that the update has arrived on your HTC One A9, make sure that you are connected to a Wi-Fi network. And you also need to make sure that your battery is charged to at least 50%.
source: AndroidPolice