The OnePlus 3 and OnePlus 3T were released three years ago, back in 2016. Both devices were launched running on Android Marshmallow but are now officially receiving the update to Android Pie. That means they have now received three major OS updates, which has to be a record in the Android space.
https://www.notebookcheck.net/The-OnePlus-3-and-3T-are-now-receiving-the-Android-Pie-update-The-third-major-OS-update-they-ll-get.422262.0.html