If you are using OnePlus 3 and / or OnePlus 3T handset here is some important news for you. Pete Lau CEO / Founder of OnePlus has confirmed that both these models will get Android O update, and that will be the last Major update for these models.
This means that OnePlus 3 and OnePlus 3T will get max up to Android O and after that they will not next Android P, however these models will continue getting security updates and bug fixes on a regular basis after Android O.
There is still a lot of time, nothing to worry about. If you may recall these handset were launched running Marshmallow and they got Android Nougat update. OnePlus 5 is the latest model and some of the features available on OP5 will not be available on OP3/3T.
How long will OnePlus 3 and OnePlus 3T continue getting OS updates?
As of now they are running Android Nougat and they will get the next Android update i.e. the Android O, and after that update, company will continue rolling out security updates. So Android O will be the last big / major OS update and OP3 / OP3T will not get next OS update i.e. Android P.
Want to know more about the OP3/OP3T check the official forum.