Two months ago Frank O’Connor, the Franchise Development Director at 343 Industries revealed the Big Team Battle would not be present in Halo 5: Guardians at release. O'Connor went into further detail, saying the classic game made would be added "shortly" after launch.
It seems as though the reasoning behind the classic game mode not making an appearance at launch is to funnel people into Halo 5's new game mode, Warzone. When asked by a fan on how 343 Industries could "reason not having Big Team Battle maps" at launch, studio head Josh Holmes replied.
According to Holmes, it's because "Warzone is the evolution of BTB, on steroids. We'll also be adding a more traditional BTB mode post-launch."
Warzone is a 12v12 game mode that features one of the biggest maps in Halo history, Apex 7. The map is an ode to Halo: Combat Evolved's Silent Cartographer and has been described by Microsoft as the following:
"Clearing out the initial Covenant threats and controlling the Forerunner Spire in the center of the island is paramount to a team's success and provides a central base of operations. If your team loses the Spire, don’t despair; players can use a system of caves or take to the beach to flank the base. Beware of the Covenant though, for they will not let you take this island so easily. They will counterattack and fight to retake their territory. Continue the push for control of the island and take out the opposition's core… before you awaken something much worse."
