Yesterday, OnePlus announced the end of the OxygenOS Open Beta program for the OnePlus 6 and OnePlus 6T, making Open Beta 6 the last beta release for both devices. However, both devices are scheduled to receive bi-monthly stability and security updates until at least mid-2021, according to OnePlus' Software Maintenance Schedule. The last stable release, OxygenOS 10.3.2, brought the February 2020 security patches, and now OxygenOS 10.3.3 brings the latest April 2020 Security Patch Level (SPL) as well as a handful of other changes.

OnePlus 6 Forums ||| OnePlus 6T Forums

Besides the April 2020 patches, the update also enables VoLTE and VoWifi support for Telenor in Denmark and VoWifi support for Reliance Jio in India. The pre-installed Google Mobile Services package has been updated to the February 2020 release and the CloudService app, which is only available in India, has been updated to version 2.0. Here's the full changelog:

OxygenOS 10.3.3 Changelog for the OnePlus 6 & 6T

  • System
    • Fixed the issue with a black screen randomly appearing while playing games
    • Updated GMS package to 2020.02
    • Updated Android Security Patch to 2020.04
    • Improved system stability and fixed general bugs
  • Network updates
    • Integrated VoLTE & VoWifi support for Telenor - Denmark
    • Integrated VoWifi support for RJIO - India
  • Phone
    • Newly added OpSports feature in the shelf
    • Added OnePlus Roaming feature: choose a plan without worrying about the SIM card when travelling
  • Cloud Sync updates [India only]
    • Updated the CloudService to Version 2.0

The update is randomly rolling out now for a small number of OnePlus 6 and 6T users according to a post on the OnePlus forums. The company is being cautious and rolling out the update to a handful of users first, and if the update goes smoothly, they will roll it out to more users in a few days. Hopefully, the update doesn't get pulled by OnePlus, but we'll keep an eye out in case there are any issues causing the rollout to be paused.

Download OxygenOS 10.3.3

Download OxygenOS 10.3.3 for the OnePlus 6: Full OTA ||| Incremental OTA from 10.3.2

Download OxygenOS 10.3.3 for the OnePlus 6T: Full OTA ||| Incremental OTA from 10.3.2

Thanks to XDA Senior Member Some_Random_Username for the download links!