Betas are hardly uncommon these days and if you're hoping to get some rounds of Halo Infinite in before launch, that's certainly a good thing. Developer 343 Industries posted an entry on the official Halo Waypoint site recently, revealing its plans regarding a Halo Infinite beta and the separate stages of it coming in the future.
The beta, mentioned in the post as "opt-in flights", will go live first on Xbox One and "may come a little later" on PC. There will be multiple stages as well, with each stage expanding the betas' size. As for when you'll be able to get some beta gameplay in isn't yet known. Read the entire post here.