Microsoft has just released Windows 10 Mobile preview build 10586.218 to members of the Insider program on the Release Preview ring
This is likely the last preview version of this build before Microsoft begins rolling it out to all Windows 10 Mobile devices. Microsoft added the Release Preview ring for members of the Insider program who wanted to get the latest stable build before it is officially made available to the general public. There's no word on what is contained in the build.
We also have confirmation that this update is rolling out to retail devices too as in non-carrier branded Windows 10 Mobile phones.