Halo: Battle Royale is not happening.
Halo developer 343 Industries has no plans to introduce a battle royale mode in Halo 5 or Halo Infinite, it seems. Halo franchise manager Frank O'Connor said on Twitter that the studio is not currently working on a battle royale mode at all. That said, O'Connor pointed out that Halo 5's Forge tools are absolutely robust enough to make a battle royale-style mode, though it wouldn't be possible for it to contain 100 players like in PUBG or Fortnite.
"We are not currently working on a Battle Royale mode," O'Conner said. "If you really want it, make a version in Customs with Elimination as a basis. Obviously it'll be compromised in terms of size, but you can make something similar now."
Indeed, a quick search of the Halo 5 custom map/mode database returns a number of different battle royale mode variants. But the difference here is that these are made by the community, and as mentioned do not support full 100-player battles.
In another tweet, O'Conner said he has "zero objection" to Battle Royale as a mode. He pointed out that Battle Royale has been around long before PUBG and Fortnite, though it is more "specific and focused" these days.
Some big-name games are jumping on the battle royale bandwagon, including Battlefield V and Call of Duty: Black Ops 4, which will have battle royale modes. Grand Theft Auto Online has had a battle mode for many months already.
All this talk about Halo having a battle royale mode appears to come back to writer Jeff Easterling, who said during a recent livestream that 343 isn't interested in battle royale.
"I'll tell you right now, the only BR we're interested in is the Battle Rifle. The original BR. So calm yourself," Easterling said, according to Destructoid.
Halo Infinite is the next game in the series. It was announced at E3 2018 through a trailer not for the game, but for the new engine that powers it. The game itself appears to still be a long time away. Halo Infinite will be free at launch for Xbox Game Pass subscribers.