Microsoft has just pushed out Windows 10 Mobile version 10586.456 to Release Preview users. As Windows Central notes, if you're on the Insider Release Preview Ring, you should be seeing this update right now on your device.
While it is unclear what this build fixes or breaks, it most likely just includes the usual under the hood bug fixes, tweaks, and performance improvements. As more information on the build becomes available we will be sure to update you! Until then, be sure to download away and comment below to let us know if you notice anything new.