- The tab icon in the browser now changes to indicate when the kernel is busy
(:ghpull:`1837`).
- Load server extensions with ConfigManager so that merge happens recursively, unlike normal config values to make it load more consistenly with frontend extensions(:ghpull:`2108`).
Remember that upgrading ``notebook`` only affects the user
interface. Upgrading kernels and libraries may also provide new features,
better stability and integration with the notebook interface.