At the beginning of July, OnePlus released the first beta of OxygenOS 11 based on Android 11 for the OnePlus 6 and 6T, ahead of its promised schedule. The phones got two subsequent beta updates, the last of them having rolled out just a couple of days ago. It looks like this build served as a sort of 'release candidate' because today OnePlus is announcing the rollout of the finalized, stable Android 11 update for these two phones. The rollout will, as always, start small. Only a limited number of devices will receive the update today, and there will be a broader distribution in a few days...
Source: https://www.gsmarena.com/oneplus_6_and_6t_are_now_receiving_the_finalized_stable_update_to_android_11-news-50479.php