Only a few days before the release of the OnePlus 5T with Nougat onboard, the OnePlus 3 and 3T flagships receive their last major software update. This Android Oreo-based update for them comes as OxygenOS 5.0.
https://www.notebookcheck.net/OnePlus-3-and-3T-receive-Android-Oreo.264184.0.html