A new blog post from the Call of Duty site says that a 30-day free trial of the Call of Duty: Black Ops 3 DLC will be released on May 30.

Yes, a free trial for DLC. DLC for a game that came out a year and a half ago. This might be the first time that only the DLC for a game was given out as a free trial before.

If, for some reason, you don't want to bother downloading this multiplayer DLC, you can opt-out using the instructions provided here.