glibmm 2.5 wraps new API in glib 2.5, and is API/ABI-compatibile with glibmm 2.4. The new API is unstable, until this become the API/ABI-stable glibmm 2.6 when glib 2.5 becomes the API-stable glib 2.6.

glibmm stays in-sync with GTK+ by following the official GNOME release schedule