Google has been working on implementing a tablet mode split screen feature into Chromebooks for some time and the functionality now appears to have been pushed to the first stable builds of Chrome OS, as first noted by Chrome Unboxed. As expected, the feature works by allowing users to pin two applications to each side of the screen while in tablet mode, with the apps then being divided by a bar that can be dragged left and right in order to increase or decrease the screen area they occupy. The system should be familiar to anyone who has previously used the split screen feature in Windows 10, though the functionality still isn't on by default and must be enabled via a flag.
Also worth mentioning is that the split screen option presently cannot be used on the stable channel in conjunction with Android apps or Progressive Web Apps, and it currently only supports standard Chrome applications. However, Google seems to be working on making this feature available to Android apps eventually, at least judging by some commits previously found in the Chromium Gerrit repository. But evidently, there's no way to determine when Google might debut split screen support for Android applications, or more to the point at hand, when the split screen functionality will be enabled on the stable channel by default. It appears that the tech giant still has some quirks to iron out first, but seeing how the split screen function has progressed from the developer channel to the current stable release via the beta channel, Google is seemingly actively developing the functionality and may have some news on the matter in the coming months.
Just like before when the split screen option was available in the earlier, less stable channels, Chromebook users running compatible Chrome OS builds will need to enable a particular flag in order to take advantage of this function, by typing "chrome://flags/#enable-tablet-splitview" or accessing "chrome://flags" and then finding the split screen option and enabling it. It now remains to be seen when Google will feel confident enough to launch this long-awaited feature to all Chromebook users.