We’ve all been working under the assumption that Windows 10 Redstone 4 would called the Windows 10 Spring Creators Update. The Spring Creators Update naming was originally unearthed during a Microsoft Bug Bash, and fit in nicely with the previous Windows 10 Creators Update (Spring 2017) and the Windows 10 Fall Creators Update (Fall 2017).
However,

Source: Hot Hardware – Windows 10 Redstone 4 Now Reportedly Called Windows 10 April 2018 Update