Epic Games has announced a brand new 50-versus-50-player game mode for Fortnite: Battle Royale. The free mode will appear as a new playlist inside the unified Fortnite client on Mac, PlayStation 4, Windows PC and Xbox One. It will only be available for a limited time, from Dec. 8 to through Dec. 17.

The new game mode will allow players to form squads with up to four of their friends, and then merge them into a random team of 50 players. Everyone on your side will appear in-game with a green chevron over their heads. Friendly fire will be turned off, and players will be able to offer aid to those on their side who have been downed but not finished off. The game will proceed until one entire side has been eliminated.

Developers at Epic tell Polygon that they hope the new game mode will provoke new and unusual uses of Fortnite’s building mechanics. Official art shared in advance of tonight’s announcement shows one team behind a wood and brick barricade fending off waves of attackers from the other team.

Epic Games’ Fortnite is a for-pay game currently in early access development. Fortnite: Battle Royale is a free-to-play multiplayer survival shooter also in early access that shares some of the same mechanics as the root game. Both titles are accessed through the same unified game client on all platforms. The team recently released a development roadmap which includes planned improvements such as new player models.

Epic told Polygon that it recently reached a new milestone over the weekend when more than 1.3 million concurrent players were logged into the unified Fortnite client. Epic was unable to say how many players were in the Battle Royale game specifically.

The company added that 30 million unique accounts have been created since launch in order to download and play the game. That includes users who paid full price for Fortnite, and those who downloaded the free-to-play Battle Royale version.