The first official stock release of Oxygen OS (OOS) based on Android Pie (9.0) is now available for Oneplus' latest flagship, the 6. As expected, the ROM contains Pie-compatible navigation and UI features, accent color change support and refreshed DND settings.
https://www.notebookcheck.net/OnePlus-6-gets-official-Pie-based-Oxygen-OS.333510.0.html