OnePlus will release an official Android 7 beta for the OnePlus 3 this month and follow with the final version in December. The OnePlus 2 will get Android 7 as well but most likely not before next year.
http://www.notebookcheck.net/OnePlus-3-Android-7-Beta-starting-this-month-OnePlus-2-will-follow.183151.0.html