Short answer
The useful part first.
GRAIN ROT supports solo play and online co-op. The developers recommend roughly four players for the intended balance, but the official FAQ does not state a hard four-player cap. Multiplayer uses player-hosted Steam lobbies, and there is currently no public matchmaking.
How many players does GRAIN ROT support?
The official FAQ says a session can support as many survivors as the host computer and network setup can handle. It also says the experience is balanced around approximately four players. That is different from claiming a fixed 1–4 player limit.
How do you invite friends?
- One player hosts a Steam lobby in GRAIN ROT.
- Invite friends through Steam, or have them join through the Steam friends list.
- Each player launches their own copy of the game.
There is no official public matchmaking at the time of this check, so the normal path is to organize a group before starting.
Can you play solo?
Yes. Solo play is officially supported, but the developer FAQ warns that it remains intentionally more demanding than co-op. Do not read “solo supported” as an automatic solo difficulty reduction.
Does every player need a copy?
Yes. The official FAQ says every survivor needs their own copy of GRAIN ROT. Steam Remote Play Together is not listed as a supported feature on the store page.