Microsoft is expected to release an Insider Build of Windows 10 Mobile this week and OneTile.ru reports that the very latest version currently in testing is 10586.29.
This is a advance on 10586.17 which was spotted earlier in the week. At various events Microsoft has indicated they hope to start the Windows 10 Mobile upgrade push-out before Christmas, and new build is expected to bring bug fixes and security updates for the final version of Windows 10 Mobile to be distributed as upgrades to the rest of the WP8.1 fleet.
Of course the Insider program will continue beyond this but the next major update to mainstream handsets outside the program will likely be many more months later.