https://www.theverge.com/circuitbreaker/2017/11/22/16690022/oneplus-5t-android-oreo-project-treble

OnePlus confirmed in its forums yesterday that none of its current devices, including the 3/3T and the 5/5T, will support Project Treble, even after they're updated to Android Oreo. Project Treble is an Android Oreo feature that attempts to address slow Android update schedules by allowing manufacturers to push out Google's most recent OS without having to wait on their chip partner, like Qualcomm, to support it.

At the time of Project Treble's announcement, it seemed that any device updated to Oreo would be eligible to support the program and that manufacturers would likely be interested in it. Now, however, it's clear that even devices running the most recent OS won't have to support the project, meaning that even if your phone’s manufacturer gives you Oreo, you aren't guaranteed a faster update to the next OS. Only devices that ship with Android Oreo installed out of the box will be required to feature Project Treble, and, disappointingly, OnePlus' most recent phone, the 5T, ships with Android Nougat. (The same goes for the Razer Phone, which was announced earlier this month.)