Halo Infinite is expected to receive its big cooperative play update in August, which will let you roam the open world with a fellow Master Chief. If you're part of the Halo Insider program—or join it ASAP—you may be able to play co-op a whole month earlier, because 343 Industries has announced a test flight for July.
You can learn how to join the Halo Insider program here, though do keep in mind that being part of that program doesn't guarantee you'll be a part of the co-op flight: You'll be "considered" for it. Still, it's free, so you're only having to contend with the drudgery of entering details into a form.
A Halo Infinite roadmap released in April pointed to a late August release for cooperative play, and so far, 343 Industries hasn't indicated any disruption to that timeline. Online co-op will roll out first, while splitscreen co-op will follow later in the year. Another eagerly anticipated addition is Halo's Forge mode, which is still on track to enter open beta in September.
Season 2 of Halo Infinite kicked off in early May, and as is so often the case with live service games, the launch was a little bumpy. It follows a fairly turbulent reception for the competitive side of Halo Infinite since its initial launch last October; after an enthusiastic uptake from starved Halo fans, the first season ended up being a bit of an awkward mess, according to Natalie.
Still, if you're like me and would prefer to enjoy some PvE action with friends, rather than getting relentlessly slaughtered in PvP, the arrival of co-op can't come soon enough.