OnePlus 5T earlier this month.
Like previous Open Beta builds from OnePlus, the Oreo-based build for the OnePlus 5 needs to be flashed onto the smartphone, requiring s to back up their devices as all data will be lost in the process. s can follow the official OnePlus flashing guide for instructions, and can the ROM from here for flashing. To recall, OnePlus has promised that the stable Oreo update for the OnePlus 5 and OnePlus 5T will be rolled out in Q1 2018, so if you are impatient to use Oreo on your device, your best bet is the Open Beta - however, do note that it is a beta build, and will have bugs that need to be ironed out.
The OnePlus 5 Android 8.0 Oreo-based build's changelog has been posted on the company's forum, and it contains Oreo features such as Picture-in-Picture, Auto-fill, Smart text selection, and a new Quick Settings design. It also brings along the October Android security patch. OnePlus specific additions include Parallel Apps, Notification Dots for the OnePlus launcher, a new app folder design, and the ability to photos directly to Shot on OnePlus.
Separately, an XDA Developers forum member last week posted what appears to be an official link to the OnePlus 5 Open Beta 2 build. Ironically, this link was posted a couple of days before OnePlus announced the first Open Beta build. A separate XDA Developers post cites a that installed the leaked Open Beta 2 build, and spotted the Face Unlock feature that the company had unveiled with the OnePlus 5T. If real, this would mean the Face Unlock feature will arrive for the OnePlus 5 with its second Open Beta build, and that s can reasonably expect it to make it the stable build next year.