While the OnePlus 3 is receiving its second beta build of Android 7.0 Nougat today, the newer OnePlus 3T apparently didn't want to feel left without an update of its own. In this case, however, we're talking about an official and supposedly stable build - and no, it's not Nougat. OxygenOS 3.5.4 is now rolling out to a OnePlus 3T near you, and it's still based on Android 6.0.1 Marshmallow unfortunately. If you were craving a taste of Nougat, you'll have to wait some more, but probably not a lot more, since the Chinese company promised that the Android 7.0 update would hit by the end of this...
Source: http://www.gsmarena.com/oneplus_3t_receives_its_first_software_update_still_based_on_marshmallow-news-22179.php