A easy question for Ci4.0 ( can i Upgrade from Ci3 to Ci4 ?)

3rd party or custom class's will be reusable if they work under PHP 7, but if you use some CI 3 features inside your custom libs, they may not work.

  Oh, so thanks you !
My Ci3.0.6 Project only use helpers and database library of CI3.0.6, another features were builted by my Team ( created in Library folder of Ci3.0.9 ! be sure ), and with your sweet answer my Project can Move to Ci4.0, now i can free about my question caption