Version 4 ships
on 9 October,
09:00 UTC.
The migration guide goes live the same morning. Everything on 3.x keeps working until April 2027, so there is no rush to move the day it lands.
Release candidate 3 is already on the public channel. If it works for you, the final build will too.
Times shown in your local timezone. The build is cut from tag v4.0.0.