From the announcement:
Now at the pinnacle of your career, you are sought after by two capital cities to build their city centers. Not only do you have to consider the natural features that were the reason for their founding, you also need to ensure the civic buildings are appropriately placed, and you must not forget to satisfy the citizens’ demands along the way.
Between Two Cities: Capitals expands the base game by adding several new challenges: landscapes, districts, and civic building tiles. This is not a stand-alone expansion; you’ll need the original Between Two Cities game to play it.
Between Two Cities: Capitals, will be released via retailers in early July with a $20 MSRP. A limited early release will happen at the UK Games Expo thanks to Board Game Extras.