Windows 1.0 April 1984 build is an early build of Windows 1.0, briefly shown in the "History of Microsoft - 1983" video. It's unknown when exactly this build was compiled, though it can be assumed from the system date displayed in the status bar at the top that it's from before 9 April 1984. It looks similar to the Fall COMDEX build, but there are some notable UI differences.
There is now a single help button on the right side of the status bar, while individual help buttons on windows have been replaced by resize boxes much like those in the final version. The date displayed in the status bar in the top left is "09 Apr 1984". The system menu button, which was previously on the right side of the status bar (where the help button is now), was presumably moved to the left side (not visible in the video as it's cut off), where it's located in later builds. Scrollbars now appear the same as in Development Release #5, and the vertical scrollbar was moved to the right side of the window. The Text applications is missing its rather crowded menu from previous builds.