Following up yesterday's release of Windows 10 build 10586.122 for PC comes the mobile version for Windows 10 Mobile.
The release is only for those on the Slow and Release Rings of the Insider program as Fast Ring is limited to newer devices (e.g. Lumia 550, 950, 950 XL) and Redstone releases as announced by Microsoft in January.
Build 122 brings stability improvements and more as noted in a forthcoming blog post. We'll update this article with more information when it goes live.
To check for updates, make sure you are enrolled in the Insider program using the Windows Insider app and that Slow or Release Ring is enabled. If you are on Redstone release (Fast Ring) you will need to roll back the OS and then take the update in Slow or Release rings.
For those on the Fast Ring but not on Restone or who are not using a Lumia 550, Lumia 950 or Lumia 950 XL you will need to switch rings to Slow or Release to get today's update.
Afterwards, go into Settings > Update & security > Phone update > Check for updates.