Today OnePlus has started sending out a new software update to the 6T. It's OxygenOS 9.0.10, and it brings with it the December 2018 security patches. Additionally, the company also promises better Wi-Fi stability for more reliable connectivity, Face Unlock improvements, and enhanced Nightscape performance for the camera. Those are all nice things to have, but obviously this isn't the biggest of updates, and there are no new features. Still, you should install it as soon as you can if only for the new security fixes. Speaking of which, the rollout is staged as usual, which in OnePlus'...
Source: https://www.gsmarena.com/oxygenos_9010_starts_rolling_out_for_the_oneplus_6t-news-34790.php