ClassicPress developers decided to break the Semver that WordPress was following. Their release page shows version 1.0.0 as the newest [1] even though their code is based on WordPress 4.9.8 [2].
They went even further to modify the content of the “version.php” file [3] which WordPress uses to control the deprecation of features in the entire project, something that the plugin ecosystem inherited by using the $wp_version
variable to check if their code is compatible with the website installation. In fact, that variable doesn’t exist anymore in their code. They replaced it with $cp_version
which seems unnecessary.
I’ll pass this to the rest of the development team.
Personally speaking, I think the warning is correct.
[1] https://github.com/ClassicPress/ClassicPress/releases
[2] https://github.com/ClassicPress/ClassicPress/blob/f059778/README.md#contributors
[3] https://github.com/ClassicPress/ClassicPress/blob/f059778/src/wp-includes/version.php#L2-L30