Once Human codes are one of the ways you can claim in-game items for free, as well as the Energy Link currency you use to do just about everything in the new open world survival game. Unfortunately, these codes don't seem to include any of the game's premium currency of Crystgin for cosmetics.
However, if the motorcycle vehicle skin is anything to go by, it seems like codes themselves will sometimes include cosmetics you can claim. I'll lay out the most recent Once Human codes below as well as provide info about how to redeem them.