On the PlayStation blog, the announcement implies that the additional Agents content will be free:
Are you ready for your mission? For PS4, we are taking a selection of your favorite Lego Agents heroes, villains, vehicles, and weapons, and placing them directly into your Worlds. You’ll be able to create, discover, explore and go on new adventures together with your friends as you create your own secret agent missions, take action in cool new vehicles, and thwart the plans of the evil mastermind Dr. Inferno.
LEGO Worlds is due for release on March 10, on Playstation 4, XBOX One and Steam.