Paradox Interactive has confirmed the first expansion for Stellaris, Utopia, will be releasing on April 6th, with the price being set at $19.99/€19.99. One of the major additions is Ascension Perks which will allow players to choose either a biological, psionic, or synthetic path for their species to travel down. The expansion will also have megastructures like Dyson spheres, and habitat stations which allow for a large population to live.
Players will also have a lot more control over the lives of the inhabitants of their territory through various rights and privileges. Decisions can be made so everyone is equal or a certain subsection of society is given more rights than others, including that of full citizenship.
Source: Press Release