This DLC release will be a bit smaller in terms of content compared to previous expansion packs for Halo 5. There won't be any new maps or gameplay modes in Hog Wild. The game's official website states that part of the reason is due to the fact that some of the gameplay additions for Hog Wild are being pushed back to the next free DLC pack, Warzone Firefight. 343 Industries says that release will be the biggest DLC for Halo 5 and it will be made available at the end of June.
In the meantime, May 31 brings the Hog Wild DLC pack, which adds four new custom Warthog vehicles to the game (Rally, Rally Scout, Sword Needler and Vespin Rocket). The DLC pack will also add new armor and weapons variants to the game. Again, it's not a huge DLC pack, but it is free, and the upcoming Warzone Firefight, with its huge vehicle battles, should make up for Hog Wild in about a month.