The OnePlus 3T was released in November last year but will not be getting any major OS updates after Android O. O is expected to be released within the next few weeks.
https://www.notebookcheck.net/Android-O-to-be-last-major-OS-update-for-the-OnePlus-3-3T.241318.0.html
Same story of update assurance when we bought OPX. Lol
so people are basically complaining that OP is giving 2 years worth of major updates when only Google does that besides them and major brands are still struggling to deliver Android 7 to some of their handsets....