Yesterday, Google announced the first Android 11 beta after months of developer previews. While it's only available for Pixel phones right now, the Mountain View firm did say that it's coming to other devices in the coming weeks. For OnePlus users, that day would seem to be today.
OnePlus has announced the Android 11 Developer Preview Program for the OnePlus 8 and the OnePlus 8 Pro. The only problem is that while there's a link to download it, it's not a live link just yet. At some point, that will link to the announcement post on its forum, and you'll be able to download the files from there. Presumably, this will happen today, since the page is live. That forum post will also include a changelog of not only what's new in Android 11, but what's coming in the version of OxygenOS that's bundled with it.
OnePlus's developer previews are pretty easy to install. After all, allowing users to customize their phones software has been part of the firm's heritage right from the beginning with the OnePlus One. All you'll have to do is download the ZIP file that corresponds to your device, and then you can go into Settings and choose the local file to update from.
Note that it's called a developer preview for a reason, and the first one likely won't be very stable. If you're not willing to deal with a lot of bugs, you might want to wait for the open beta program.