As well as rolling out the Windows 10 October 2018 Update to general Windows users yesterday Microsoft have also pushed out the update to HoloLens. The build number is 17763 and was first rollout out to Windows Insiders at the end of September.
The October update (1809) has many new features. There any many improvements to the user interface, Miracast streaming, new notifications and sharing improvements. The update is a mandatory update for the HoloLens and well worth having.
Here is my hands on look at the October 2018 Update for HoloLens: