Subnautica currently features four different Game Modes. The player can select a Game Mode when starting a new save file; a save file's Game Mode cannot be changed after the save file is created. Each Game Mode imposes different restrictions (or lack thereof) on gameplay.
To stay alive, the player must manage their health and oxygen levels. If the player runs out of either, they die and lose all of the items in their inventory. The player can return to where they died to reclaim their lost items. The player can "secure" their inventory by entering Lifepod 5, a Seabase, or a Cyclops; if the player dies with a secured inventory, they will keep all the items from the last time their inventory was secured and will respawn in the last place they secured their inventory.
Similar to Freedom Mode, but the player must also maintain Food & Water levels in addition to health and oxygen. If the player runs out of either food or water, they will begin to lose health until they die.
Similar to Survival Mode, but restricts the player to a single life only; if they die, the game ends, forcing them to completely start over from the beginning. In addition to this, the PDA will not warn the player when they have low levels of oxygen.
Story, health, oxygen, hunger, and thirst are disabled, materials and Blueprints are not required for crafting, and vehicles and Seabases do not require Energy to operate and cannot be damaged. This is a sandbox mode for players who want to freely explore and build.