Pax Expanse is a retheme of Pax Pamir (designed by Cole Wehrle) to The Expanse universe, covering the first three seasons of the TV show. Most of the core mechanisms are identical to Pax Pamir, though some have been tweaked to fit more appropriately to the Expanse setting.

In the game, 3-4 players act as powerful puppetmasters acting behind the scenes of the Solar System, manipulating the three main factions to their own advantage: The United Nations, the Mars Congressional Republic and the Outer Planets Alliance. All while mysterious events are occurring due to the arrival of the extraterrestrial Protomolecule.

Gameplay is mostly in the form of area control. However, each area of the board can be controlled in two different ways (often simultaneously): a faction can control a region by having the most fleets and transports there, whereas a player can control a region by having the most supporters and fleets of a faction they are loyal to present. Four scoring phases occur throughout the course of the game, and the method of scoring is determined by whether any one of the three factions is in dominance when the scoring occurs. If so, then players loyal to the dominant faction will score victory points. If not, then players score victory points based on their individual power and presence on the board.

Players can increase their power and abilities by purchasing asset cards from a communal market using influence, the game's currency. Each asset grants its controller particular actions and abilities, and at any particular time one of the four types of cards - Military, Subterfuge, Political or Economic - will be able to perform their actions for free based on the current political climate.

Players must acquire the most powerful assets, ally themselves with the ascendant factions, and make deals with other players to secure their positions on the board and score the most victory points when the scoring phases occur. After four scoring phases, the player with the most victory points is the winner!

Cole Wehrle (designer of the original Pax Pamir) has indicated that he has no objection to the files for this game being shared on BGG.

—description from the designer