Zombie modes in big action games have been popular for a very long time, and now it's Halo Infinite's turn with Survive the Undead. This is a new PvE mode developed by The Forge Falcons (created with Forge by fans), and 343 Industries obviously thinks it's good enough to promote.
It's a Horde-inspired mode where you have to survive as many rounds as possible against an increasingly fierce enemy, with the record currently standing at round 64. Via Halo Waypoint, The Forge Falcons describe their game mode like this:
"Survive the Undead is an all new, endless, round-based horde mode. Made with Halo Infinite's Forge tool, it takes full advantage of Halo's sandbox and gives players a PvE experience they haven't seen in Halo before."
Survive the Undead will be available for two weeks, so be sure to try it out, judging from the comments it is very well received.