Ghosts of Meridian is shipping today to Halo 5 owners and with that 343 has revealed that there will be a beta for Warzone Firefight.
In case you didn’t know about Warzone Firefight here is a brief description:

Warzone Firefight is an ambitious new multiplayer mode coming to Halo 5: Guardians that stands primed to offer the biggest Halo cooperative experience ever in franchise history. In Warzone Firefight, up to eight players will work together to complete five rounds of increasingly difficult, dynamic objectives set against a timer to emerge victorious.

The five-day beta experience will see Spartan fireteams of up to 8 players battle against an onslaught of enemy AI on the Escape from A.R.C. Warzone map. Players will have full access to their Halo 5: Guardians REQ’s.
343 has also revealed a new promotional pack – the Mythic Warzone REQ Pack which will help fans get the powerful weapons easier than trying to open a regular gold pack.