The Arena modern Black Ops 3 features two different playlists, the Pro Series and Moshpit. Pro Series features the full competitive experience, with specialist draft, ban and protect, and more. 

Images from the mode reveal that the Pro Series features Search and Destory, Uplink, and Hardpoint as of now. The description also reveals that playing in Arena will still count towards progressing your character, with earning XP, Cryptokey, and more. All content is unlocked for all players in Arena, so that there’s no barrier of available equipments/weapons amongst players. 

In addition, Arena is based on skill based matchmaking. 

As announced earlier, the season of Arena running this month is a beta season. Treyarch will finalize all of the details during this season.