install over version 2.8

Hello, I would like to know if it'a possible to install the new version over the version 2.8 ?
Are config files compatible ?
Is the classic ladder compatible ?

Is the gui of the classic ladder better in version 2.9 ?

what are the main difference of the new version ?

Best regards
Thierry Vorms

Details and instructions for updating from 2.8 to 2.9 are covered in the doccumention. I don't think there were any significant configuration changes, and none that would be incompatible with a 2.8 config.
linuxcnc.org/docs/stable/html/getting-st...dating-linuxcnc.html

I don't think there are or were any changes in Classiclader for version 2.9

Change log for 2.8 to 2.9 is here.
linuxcnc.org/2023/11/04/LinuxCNC-2.9/