The finalized version of the update is headed to the company's two handsets from last year. It arrives as OxygenOS 9.0.0, based on Android Pie. It contains the December 2018 security patches too.
When you get the new software, you'll see the brand new Pie UI, new navigation gestures for the 5T, and you get a new Do Not Disturb mode too, with adjustable settings. Google Lens is integrated in the Camera app, and Gaming mode 3.0 comes with a text notification mode and added notifications for third party calls.
Obviously some unnamed system improvements are baked in as well. As usual, the rollout is staged. It's going out to a small percentage of users at the moment, and it will expand in a few days.