The API is now frozen. Only incredibly important API changes will be allowed before the final fully-frozen gtkmm 2.4.0 release on April 12th.

gtkmm 2.3/2.4 installs in parallel with gtkmm 2.2, so you can install thisunstable library without the risk of breaking existing applications. This allows us to break ABI and API, though we will try not to break API unless it is absolutely necessary.