Battlefield 4 just received a brand new UI update.
Battlefield 4 finally received the long awaited UI update.
You can now download a 5GB update for Battlefield 4 which will give you access to a BF4 version of BF1 menu, from which you can join servers, play on Test Range, play campaign and many more other stuff.
You can also join a BF1 server straight from the menu (that will close BF4 and open BF1).
Note: As of this very moment there is no way to join a BF4 server via BF1
Here you can see what the menu looks like: