Windows 10 '19H1' will be known officially as the May 2019 Update and should begin rolling out to the public in late May.
Microsoft today announced that the next Windows 10 feature update, codenamed "19H1" and known as version 1903, will be called the Windows 10 May 2019 Update and will begin rolling out to the public starting late May. This is the first "May" update for Windows 10 as previous spring releases always launched in April. While the May 2019 Update was finalized on time, Microsoft is giving it an extra few weeks in testing, to ensure everything is working as intended.
Full story from the WindowsCentral blog...