OnePlus recently announced that it has started to roll out the OxygenOS 4.0 update to OnePlus 3 and 3T. The OxygenOS 4.0 has one most notable feature/change and that is Android 7.0 Nougat and with it, it has a number of other changes such as new notifications style, multi-window support and a clean and organized Settings menu. In addition to these Status bar icon options and shelf customization is also added in OxygenOs 4.0.
The update has started to rollout via OTA and a broader update will be releasing soon. If you want the beta then OxygenOS Open Beta is also available for OnePlus 3T. Before you can apply the update, flashing is a must and there could be a lot of bugs in the beta so, think before loading a beta update.