It's widely expected that Insider Preview build 17134 will become the fabled 1803 release, but even that is not yet official.
UPDATE: Microsoft finally announced, late on Friday night, that build 17134 will become the "April 2018" Windows 10 update; that update being made available to download on Monday 30th April (so only just keeping to April, eh). The build version is *still* 1803 rather than 1804 or almost 1805; but hey, at least it's finally here!