Ah yes, "Will they or won't they?", the now to be expected affair between ongoing FPS series and the popular battle royale format. Halo Infinite's developers previously expressed disinterest in plopping a hundred Master Chiefs into a last Chief standing mode but a new rumor has cropped up saying they will—and that it's coming in 2021.
A rumor posted in October by the "Gaming Leaks & Rumors" account on Twitter partially based on a Reddit post is currently going around. The poster claims that 343 Industries plan to release a free battle royale mode set on the Zeta Halo ring sometime in 2021. The same source also claims that Halo Infinite will release four total campaign chapters over the next decade, beginning with the launch in 2021. It also claims two spinoff games are in the works including Halo Wars 3. According to the Twitter thread with additional details, 343 are testing two possible endings for Halo Infinite.
As ever with alleged leaks, several grains of salt would be healthy here. The rumor does incorporate some details that 343 have alluded to about Halo Infinite's future though, which are worth a refresher while we wait to hear more official news from 343.
We do know that Halo Infinite's multiplayer will be free-to-play and they have indeed described Infinite as the start of the next ten years for Halo and "a platform for the future". 343 haven't been clear on what exactly that means, so I suppose new campaigns are a valid guess.
As for the battle royale mode, 343 seemed pretty staunchly against one in 2018, with writer Jeff Easterling saying "the only 'BR' we're interested in is the 'Battle Rifle.' The original BR. So, calm yourselves.". In 2019 though, studio head Bonnie Ross gave a less firm answer. "Whatever we do needs to be the right thing for Halo. Whether or not you call it a battle royale or how we're thinking about things going forward, the team thinks about, 'This needs to be right for Halo,'" she said.
Whatever their current plans, 343 have almost certainly talked about the possibility of a battle royale mode. They, like all other FPS series developers, are aware of Fortnite and Apex Legends and Call Of Duty: Warzone. Whether or not they've decided that 99 Master Chiefs all dropping out of a plane and zapping one another is the right move for Halo, we'll just have to wait and see.
343 Industries have said they're planning an update on the status of Halo Infinite to clue their fans in before the end of the year. They also say they're planning to be "much more communicative in the coming months".
Infinite was planned for launch this year with Microsoft's new Xbox boxes but, after a delay, is now planned for sometime in 2021.