This update actually brings a couple of new features to the two devices, along with a new security patch, and optimizations. Before we proceed, do note that you'll need to have Open Beta 2 installed in order to successfully update to Open Beta 4.
OnePlus urges users who do not have Open Beta 2 installed, to first install it, before proceeding with Open Beta 4. If you do not have Open Beta 2 installed, and you proceed with updating straight to this version, the update will fail.
OxygenOS Open Beta 4 brings a December 2019 security patch to the OnePlus 6, 6T
Regarding the update itself, it brings the Android security patch for December 2019 to both devices. OxygenOS Open Beta 4 also brings a feature to support reminders for privacy alerts to the OnePlus 6 and 6T.
Ringtone increasing and decreasing features for incoming calls have also been added. On top of that, the company has improved the Reading Mode on the two devices.
OnePlus has added a fresh new chromatic effect for a more immersive, and comfortable reading experience. This mode comes with smart color gamut, and saturation adjustment.
You can access new Reading Mode features by navigating to Settings, then hitting the Display option. There, you will see the 'Reading Mode' menu, from which you can flip the switch on this new feature.
The 'Emergency Rescue' feature has also been optimized
The company has also optimized details for the Emergency Rescue feature, and improved system stability on the two devices. General bug fixes have also been listed.
That is pretty much it as far as the changelog is concerned. Before updating, do note that this is just a beta software. You may encounter some issues / bugs with it, so proceed at your own risk.
If you're already running Open Beta 2+ software, you can update to Open Beta 4 OTA. If not, please update to Open Beta 2 first, as mentioned earlier in the article.
If you're running on a stable channel, and would like to switch, that is rather easy to do. You'll need to download a beta package, and simply install it on your phone, from the device. Do note that getting back to the stable channel will require you to factory reset your phone.
That is pretty much it. We still do not know how large this update is. Chances are it weighs a couple hundred MBs, though that's just an estimate on our part.