OnePlus has been very open and fast with their Software updates, however they have been dropping some smartphones out the update list very fast, like the OnePlus 2, and OnePlus X. And with the release of the OnePlus 5, users with the 3 and 3T are very nervous about the support for their devices.
OnePlus’s Head of Product, Oliver Z., has announced that Android O will be the last major Update for the OnePlus 3 and OnePlus 3T. However, he did go on to say that the devices will receive security patches and app updates will be rolling out for the foreseeable future. Once the OnePlus 3 and OnePlus 3T get the Android O update the Open Beta Program will be migrating to the OnePlus 5.
Talking about the future updates, the OnePlus 3 and 3T will be getting the August security patches very soon, and the 4.5 build of the OxygenOS will be rolling out in the next couple of months. While the 3 and 3T might be running the same version of OxygenOS as the OnePlus 5, there are some hardware centric features that might not be available on the 3 and 3T, dude to hardware limitation or just for the sheer capability of the devices. Some of these features might be, Reading mode, Gestures while the screen is off, DCI-P3 screen calibration etc.