The OnePlus 3 is a pretty great device by any measure, but shipped out with Android 6.0.1 (Marshmallow), instead of the latest version, Android 7.0 (Nougat), since it came out before Nougat was made official. For some devices, a beta update is available, which brings the Android version up to Nougat. The newest version of that beta update is OxygenOS version 9, and it is now available for all OnePlus 3 owners. Earlier versions of the beta brought users all the Nougaty goodness they expect from the latest version of Android, and this newest update keeps the tweaks and fixes flowing, and even manages to add in a new feature in the form of expanded screenshots.
The headlining feature change for this update, being the expanded screenshot feature found in some versions of Marshmallow on OnePlus devices, allows users to take a screenshot of the entire contents of their current screen, such as a whole web page, rather than just what's currently viewable on the display. The update also brings a few optimizations and tweaks to the general user interface and the design of the shelf. Performance and stability enhancements are also on board, as are battery and display resolution and DPI optimizations. A generic "general bug fixes" caps off OnePlus' post about the new beta update, and posts from OnePlus 3 owners on the forum aren't making it clear what bugs were squashed.
The update is currently rolling out over the air to all OnePlus 3 owners who are already on a Nougat-based beta software, but those on other software, such as official Marshmallow or custom ROMs, will have to fresh-flash the update through ADB. If you happen to be on a beta firmware and can't see the update, a reboot may do the trick, but if not, you'll just have to wait for it to hit your neck of the woods. Users currently on the beta can always fresh-flash using ADB and the files posted on the forum, of course, if they don't want to wait. Those who want to hop on the open beta should be warned that they won't receive stable software updates anymore, and will have to flash back to stock in order to hop back over to that train of updates. If that doesn't deter you, head through the source link to grab the firmware and get flashing.