Steam players will be sent a unique key to dive into the relevant build through Halo Insider.
Halo Infinites campaign co-op test will support up to four players across PC, Xbox and Xbox Cloud Gaming.
343 say that the chance to replay missions is also coming along with campaign co-op.

The way 343 have got round this is by using the games tactical map, or tac-map.
Replaying a mission resets it and teleports you to its starting location.
Hey Presto, Big John Halos your uncle.

Brendan was glad to have an open-world to explore in hisHalo Infinite review.
It has taken the series a while to look outside its corridor shooting monoculture for inspiration, he said.
The campaign co-op beta for Halo Infinite is due to land sometime this week and lasts until July 22nd.
The full co-op and mission replay launch is expected in August.
Theres more info about what’s coming on the Halo Waypoint sitehere.
Are you happy at the idea of finally teaming up with other Spartans?