Succeeding GNOME 3.38 Will Be "GNOME 40" - Yes, GNOME Forty
Not GNOME 4.0, but GNOME's new versioning scheme is jumping next to GNOME 40.0. Stable point releases will go on as GNOME 40.1, 40.2, 40.3, etc.
Every six month release to GNOME will bump the major version number meaning GNOME 41 will be coming around this time next year.
As part of the development cycle the pre-releases will be as GNOME 40.Alpha, GNOME 40.Beta, and GNOME 40.RC. This is dramatically fewer development releases than currently in the GNOME land.
The developers decided to change the versioning scheme due to the GNOME 3.xx minor version "getting undwieldy", not going to GNOME 4.0 to avoid confusion with the imminent GTK 4.0 release, and other reasons.
Those interested in more details on this versioning change at GNOME Discourse.