The Expanse: Osiris Reborn will not use fixed character classes, instead allowing players’ combat styles to be defined mainly by their equipped and upgraded weapons and gadgets. Although players choose an initial specialisation, it only determines starting abilities and equipment, leaving scope to build hybrid characters as the game progresses.

Captains can invest in four open skill trees: Marksmanship, Gadgets, Survivalist and Leader, covering weapon handling, abilities, durability and companion support. Players cannot unlock every option, but can reset their build aboard their ship for an increasing cost; gear upgrades at a workbench range from basic stat improvements to new effects and abilities, such as a frag grenade firing additional explosive projectiles.