Few Android OEMs update their devices for as long as OnePlus does. Released in 2016, the OnePlus 3 and 3T have received three major OS updates bringing them from Android 6.0.1 Marshmallow up to Android 9.0 Pie. However, both handsets have now started receiving their final software updates, as we wave goodbye to the devices that brought OnePlus into the mainstream.
https://www.notebookcheck.net/OnePlus-issues-its-final-update-to-the-OnePlus-3-and-3T.443261.0.html