Microsoft has unexpectedly pushed out Windows 10 Mobile build 14356.1000 for those on the Fast Ring of the Insider program.
This update follows the one last week for Windows 10 on PC. The previous Fast Ring Mobile build was 14342.1004. There's no word yet from Microsoft on what's new in this version, and it's possible it's rolling out ahead of schedule. For now, just head to your Settings > Phone Update and Check for Updates to grab the new build.
Thanks to everyone for the tips!