OnePlus 3 and 3T have just received the latest Nougat-based Hydrogen OS 3.0 update, which brings a couple of additional features and enhancements over the Oxygen OS. For starters, you get an enhanced battery life while updating from Oxygen OS along with a new call recording feature.
Although the ROM is limited to the Chinese variants of OnePlus 3 and 3T, it can be easily installed via recovery in both Chinese and English languages. There is no Google apps included with this package and you may want to delete the extra Chinese apps to free up some space on your device.
The ROM is available for download via official OnePlus website as well as through XDA Developers portal. The XDA offers you two options wherein you could directly install the ROM via Play Store installer or sideload it from your PC for a clean installation.
[Source: OnePlus via XDA Developers]