Today, Microsoft is releasing Windows 10 Insider Preview build 20277 and 21277 to the Dev channel. If you thought that it was confusing with the team switching to the fe_release branch for a fake update, then it gets even better. Build 20277 is still from the fe_release branch, while build 21277 is from the rs_prerelease branch.
Everyone is going to get build 20277 by default, but Microsoft wants to give people the option to switch back to rs_prerelease builds, presumably what they signed up for. You'll see the option to take build 21277 as an optional update. Once you enroll for rs_prerelease, you can't go back to fe_release, which should be fine since fe_release isn't a real update.
That's because build 21277 comes with a hotly anticipated Windows on ARM feature: x64 app emulation. Microsoft confirmed that it was coming a couple of months ago, and while it was originally planned for November, it arrives today.
Aside from x64 emulation, build 21277 comes with support for Unicode Emoji 12.1 and 13.0, adding things like bubble tea, smiling face with tear, ninja, magic wand, and more. There's also a focus on gender-neutral emoji characters with this update.
While build 21277 is from the rs_prerelease branch and therefore isn't tied to a feature update, you might be expecting all of this to land in 21H2 next year. Some features could be ported into 21H1 if Microsoft chooses to do it, so we'll have to see what happens if and when the firm starts testing 21H1 in the Beta channel.