You need the base game though
Square Enix has shifted the free weekend for Final Fantasy XIV: A Realm Reborn around a bit. Instead of taking place last week right after patch 2.3, the free period is going to start on July 18th, and run through July 21st at 12:00AM PST.
The bad news is that you'll need to own the game already to play, so this campaign is basically open to people who have the game but also have an inactive service account. So if you quit a while ago and want to see what patch 2.3 has to offer, check it out.
Announcing the Free Login Weekend! [The Lodestone]