OnePlus often releases Open Beta versions of its Android skin, OxygenOS. They are often updated compared to the "normal" (stable) builds in terms of features, security patches and other new tweaks. The OEM has started just such a program for its latest flagships, the 7T and 7T Pro.
https://www.notebookcheck.net/OnePlus-announces-the-7T-and-7T-Pro-s-first-OxygenOS-Open-Beta.457474.0.html