Owners of the HTC One M9 on Verizon are now starting to see the Android Marshmallow update roll to their devices. The updated software is version 3.37.605.7 in Verizon numbering convention and brings the M9 up to Android Marshmallow 6.0. If you remember, HTC rolled out the Marshmallow 6.0 update to the unlocked variant of the M9 back in December. Those devices have subsequently been further updated to Marshmallow 6.0.1 so yes, this update from Verizon is behind in security updates and features. Still, it’s here at that is very much a positive sign.
As for when your One M9 will see the update, it could be as early as today or as last as a couple of weeks. As with all of these updates, the carrier is rolling the update out in phases so not everyone is going to get it immediately. The best thing to do is wait for the OTA to hit your device. When you do get notified, you will want to make sure you are on a Wi-Fi connection to download the near
1GB installer and your phone will reboot during the upgrade process at least once. You will also want to make sure your phone is connected to AC or has a near 100% battery charge on it before starting the upgrade.
You can manually check for the update by going to Settings>About Phone but doing so does not mean you will get it a that time.
In the software update notification on the Verizon site, there is nothing specific that the carrier is adding to the build like other carriers have done.