Seamless Co-op Guide: Seed Setup & Turn-Taking

Seamless co-op enables two players to share the same Oxygen Not Included world and play together on a single asteroid seed with synchronized progression, duplicant control hand-off, and consistent world generation. It matters because it preserves map identity (world seed), resources, and long-term base state so both players experience one continuous game rather than independent saves.

How seamless co-op works

• The world is defined by a single alphanumeric world seed. Entering the same seed reproduces the identical asteroid layout, biomes, and initial placements for any player who joins later.
• Players share the same simulation: buildings, resources, duplicants, and research progress are common and updated in real time for both participants.
• Co-op sessions are effectively one persistent save file. Any change made by one player is visible to the other; there is no separate instance per player.

Starting a co-op game

• Create or host a session using the desired world seed. If you want to replay or share a previously enjoyed asteroid, copy its seed and enter it when creating the new world to get the exact same map layout.
• Special asteroid types (accessed via The Lab) can have unique world seeds; these seeds reproduce those special asteroids when used.

Sharing control and playstyle considerations

• Duplicant assignment: both players can interact with and give orders to the same set of duplicants. Coordinate task priorities and scheduling to avoid conflicting orders.
• Base planning: because the world is shared, plan building placement, pipe/gas networks, and power grids together to avoid undoing each other’s work.
• Resource management: stocks (food, materials, oxygen, power) are communal. Set explicit roles or responsibilities (e.g., one player focuses on plumbing and power, the other on farming and research) to streamline progress.
• Time-sensitive operations: when performing high-risk tasks (e.g., opening a new biome, exposing volatile gases, or beginning a rocket launch), announce intentions to your partner to prevent accidental disasters.

Reproducing and sharing maps

• To replay a favorite asteroid or to allow a friend to join the same layout later, copy the world seed string from the host save and give it to the other player. Entering that seed when creating a new world yields the same asteroid arrangement and biome distribution.
• Note that while the seed reproduces terrain and biome placement, any persistent state from a previous multiplayer save (built structures, researched tech, progressed missions) does not carry over—those are part of the save file itself, not the seed.

Special seeds and The Lab

• Certain special asteroids have predefined seeds accessible through The Lab game mode. Using those predefined seeds places you on those special asteroid types with their unique biome compositions and starting conditions.
• If you want to play a special asteroid later with a friend, use that special seed when creating the session so both players start on the same special map.

Practical tips for smooth co-op

• Communicate continuously: use voice or text to coordinate construction, exploration, and crisis responses.
• Assign clear responsibilities: split base tasks (power, plumbing, research, exploration) to avoid overlap and improve efficiency.
• Use shared markers: mark areas for future expansion, resource stockpiles, and high-risk zones to make intentions explicit.
• Backup saves: because the world is shared and persistent, periodically export or backup the save to prevent loss from accidental mistakes.
• Recreate maps intentionally: when you want another playthrough with the same layout but fresh state, create a new session using the same seed rather than copying an existing save.

Limitations and behavior to expect

• The world seed guarantees the same asteroid layout but not the same dynamic state; co-op is a single live game rather than two synchronized but independent games.
• Special-seed asteroids are seeded uniquely by The Lab and should be used directly to reproduce those experiences.
• Session-specific progress (buildings, conquered challenges, duplicant experience) is saved in the save file and must be shared rather than recreated by seed alone.

Seamless co-op lets two players experience a single continuous ONI world together while preserving the exact asteroid geography via world seeds; successful co-op requires coordination, clear role division, and occasional save management.