After the OnePlus 7 series and OnePlus 7T Pro, OnePlus 7T has started receiving OxygenOS update with January 2020 security patch. Indian users are getting the OxygenOS 10.3.1 update, whereas global users are receiving the OxygenOS 10.0.8 update.
The latest OxygenOS update for OnePlus 7T brings Wi-Fi calling support for Jio subscribers in India. It also includes improved system stability and general bug fixes. It optimizes the RAM management and improves blank screen issues with some apps. Several changes have been made to the Work-Life Balance mode as well.
The update is rolling out over-the-air. Users can also check for the update manually in Settings.
Source: OnePlus forums