Starseeker supports up to 4 co-op players. The clearest listings I found say “up to four players” and show online co-op for 2–4 players, so 4 is the max for a squad.

Quick Scoop

  • Max party size: 4 players.
  • Online co-op range: 2–4 players.
  • It’s built around team expeditions, so it’s clearly designed for small co-op groups rather than large lobbies.

TL;DR: Starseeker is a 4-player co-op game.