The update seems to not include much information other than the fact it comes with the December 2019 security patch, stability improvements and bug fixes. Strangely, OnePlus hasn’t officially announced the update on its website. The update comes in at 425MB.
The OnePlus 5/5T will get the Android 10 beta in the second quarter of this year, which means owners will be waiting for a few more months.
The update will likely roll out in stages, with new OxygenOS updates. You can grab the OTA file update from the Oxygen Updater or head to Settings.