GTK+ 3.11.4 adds GtkActionBar, which is a new container for places where header bar theming is not suitable. GTK+ 3.11.4 also has improvements to GtkAppChooser with simplified and modernized online support, GtkHeaderBar theming is now more flexible, there's numerous accessibility improvements, the Raleigh GTK theme has been updated with new features and client-side decoration support, and a new "hidden-when" attribute for model-based menus.
There's also a ton of bug-fixes found in GTK+ 3.11.4. More details on this GNOME tool-kit update can be found via the project's news file. Overall there's many GNOME 3.12 changes landing to make for an exciting official release in March.