Microsoft has released Cumulative Update Build 16232.1004 to Windows Insiders in the Fast ring running Build 16232.The primary goal of this update is to test our servicing pipeline. This update should not require you to have to reboot unless you happen to have Notepad.exe open. This update only revs the version of the OS and includes a updated binary version of Notepad.exe and nothing else.
My personal view:
This is a very small update which is more for Microsoft than you. Actually this minor update will make the road better for Windows 10 Fall Creators Update.