EA revealed the expansion in a blog post; saying, “What happens when the lights go out, and criminal and police factions are forced to face off under the slimmest sliver of light? Find out yourself.” 

The Blackout is centered around the theme of, as EA describes, the cloak of darkness. In more blunt terms, it is a night themed expansion. 

EA also released a list of features that the expansion will include:

Two maps: Night Job and Night Woods (night versions of Bank Job and Backwoods) 1 new gadget: Night Vision Goggles 2 new weapons for all classes and factions: a new version of the RO933 and a new Battle Rifle New music, camos, assignments, patches, and more

There will also be a variety of game play improvements, including improvements to the Spectator mode of Battlefield Hardline. No specific details were released.

Battlefield Hardline will have additional adds-ons, Getaway and Betrayal, released sometime during 2016.

New Battlefield Hardline Free Expansion  Blackout  Announced   Battlefield  Hardline - 54