Subnautica’s save unit is a slot directory. Each slot contains several records describing world and player state, which means a backup made from one selected file can be incomplete. The safest procedure is to close the game and copy the entire `SavedGames` directory or the complete slot you care about. Storefront matters because the base path can change—particularly between the standard game directory and the Epic LocalLow location.
For this PC reference, the documented storage is Windows: Standard Windows: <path-to-game>SNAppDataSavedGames
Epic: %USERPROFILE%AppDataLocalLowUnknown WorldsSubnauticaSubnauticaSavedGames | macOS: $HOME/Library/Application Support/unity.Unknown Worlds.Subnautica/Subnautica/SavedGames | Linux / Steam Play: Steam Play: <SteamLibrary-folder>/steamapps/compatdata/264710/pfx/. The known file or folder pattern is slot0000, slot0001, … save directories. Subnautica uses slot directories rather than one portable save file. A slot contains multiple binary/metadata records, so preserving the full slot folder is safer than selecting one .bin file.
Backup guidance: Copy complete slot directories or the entire SavedGames folder. Do not back up only the most obvious binary file inside a slot. Cloud support depends on storefront. The local slot directory should still be backed up before game updates, mods, or migration. Launcher and cloud context matters because PCGamingWiki documents different Windows locations for standard installs and Epic. Microsoft Store packaging should be treated separately when the standard SNAppData path is absent.
Compatibility and recovery should stay conservative. A slot folder is a coordinated set of files. Mixing parts from different slot revisions can create a state that was never produced by the game. If the expected progress is not visible, If the expected SNAppData directory is empty, identify the storefront and check the documented Epic LocalLow path. Keep older slot copies intact while diagnosing. SaveEditor.com only labels a game-specific editor as available when a separate linked Tool has a verified operational runtime; this reference page by itself is not an editor claim.