The Halo Infinite Act of Genesis stance is one of the game’s multiplayer customizable stances, a nod to the cover art of Halo 5: Guardians.
You’ll pick your customizable stance from the Customize > Spartan ID > Stance menu. In this menu, you’ll see all the stances available in the game, along with a note about how to unlock them (though most of them currently read “Stay tuned for more details”).
The Act of Genesis stance says that it’s “Available in Halo Infinite’s Campaign.” As yet, though, no one has been able to unlock it. Most players assume that the Act of Genesis stance would unlock upon completing the campaign on Legendary difficultly, but it doesn’t seem to work (yet?).
Others reported collecting every audio log, Spartan Core, Skull, and Mjolnir armor locker, or even earning every one of the game’s 119 Achievements — which include things like freeing every FOB and responding to every UNSC distress signal — but the Stance still hasn’t been unlocked.
We’ll update this guide once the method for unlocking this Legendary stance is discovered.