For your information, Project Treble is an Android Oreo feature that addresses slow software update schedule of handsets. This feature also enables users to flash AOSP GSI (Generic System Images) onto your device. Besides, Project Treble, OxygenOS Open Beta 13/11 also includes various other new features and fixes.
OxygenOS Open Beta 13/11 Changelog: The update is now rolling out through OTA for beta participants. If you would like to install OxygenOS Open beta manually and want to enjoy the latest features on your OnePlus 5 or OnePlus 5T, then you can download and install the full ROM. Download: You can use the Oxygen Updater app to get the OTA update right now or use any VPN app and set the region to Canada or Germany to get early. You can also download latest OxygenOS Open Beta builds from OnePlus download section here. After downloading the update file, install the update via stock recovery as described here. Keep in mind that since this is a beta OS, it is possible you will run into bugs and other instabilities. (Source – OnePlus)
