There’s been a rumour for a while that Certain Affinity is working on a Halo Infinite battle royale, and the studio has recently promised that the project it is working on is “something big and new for the franchise.”
That obviously never happened, but frequent Halo assist studio Certain Affinity is working on something to do with Halo Infinite, and there are plenty of rumours that that is where the battle royale mode is being developed.
Obviously we still don’t know what exactly it is that Certain Affinity is working on, as so far the battle royale rumours are just that.
Back in August of 2020, the Halo Infinite store page made a mention of a battle royale mode, and later that year a rumour emerged that suggested the game would in fact be receiving such a mode sometime in 2021.