Unlocked HTC 10 gets a new software update, system and security enhancements included
According to HTC, the update includes system enhancements, as well as a "security update by Google" (most likely, this means the December security patch).
There's not much else that HTC is sharing about this update, but you'll probably notice some changes once you download and install it. Mind you, this is an over-the-air update (like most software updates these days) and it may not be available to everyone today.
You can manually check if you can get the update on your unlocked HTC 10 by going to Settings -> About -> Software updates -> Check now.
As a reminder, carrier variants of the HTC 10 won't be getting Android Nougat (or any substantial software update) before early 2017.
source: XDA forums