Now through January 3rd!
From the announcement:
Capture - the newest addition to the collection of team-based modes in Grand Theft Auto Online, is now available as part of the latest free automatic update on PlayStation Network and Xbox Live. With 20 new Jobs across four unique modes, this GTA twist on classic capture the flag style confrontations brings a whole new level of adversarial action to the world of Los Santos and Blaine County. Strategy plays a huge role as you run decoys, set traps and place obstacles to ensure your enemies don't get close to your goods.