OnePlus has just posted download links for its latest Developer Preview (DP3) for the next upcoming major Android update. It contains the latest features of both this OS and OxygenOS, the OEM's custom skin for the same. This build of DP3 is compatible with the OnePlus 7 Pro, 7, 6T and 6.
https://www.notebookcheck.net/OnePlus-releases-Android-Q-Developer-Preview-3-for-the-7-and-6-series.427924.0.html