Subnautica's version map is best read as three eras. Legacy — everything before the Living Large update of December 2022, when the game moved to a newer engine generation and the entire QModManager mod ecosystem died at the door. 2.0 — Living Large onward, where modding rebuilt on BepInEx. And since autumn 2025, a schism inside 2.0: the Unity security patch that swept the industry hit Subnautica too, breaking "nearly every modern mod (again)", as the community's revert guide puts it — so even current-era modders now pin the August 2025 build. Around those three sit two boutique publics: speedrunners, whose category standard is a September 2018 build, and archaeologists of the December 2014 early-access original. Paid game, single-player, no anti-cheat — the only rules here are engineering.

01The official Legacy branch

Unknown Worlds left one door open themselves: the legacy branch in Steam's Betas tab holds the last pre-Living Large build — the era where your 2021 saves and the classic QModManager mod library live. Two honest notes from the developers' side of the fence: they've pointed to a security issue in the old build as the reason deeper version access stays restricted (more on that theme in section 04), and the legacy build ships with its era's bugs preserved, like the infamous Prawn-through-the-floor in the endgame facility. It's a museum piece, displayed as found. GOG and Epic copies don't get the branch — the Steam-infrastructure lesson as usual.

02Depot recipes for the rest

Everything the one branch doesn't cover is depot work, and Subnautica's community guides maintain the codes openly. Windows lives in depot 264712, macOS in 264713; the eras people actually request, by date: the Legacy-final build (December 7, 2021), the pre-Unity-fix 2.0 build (August 12, 2025 — verified manifest 8427274798903478123), the speedrunner build (September 30, 2018) and the early-access original (December 16, 2014). The current guides demonstrate the Steam-console route; the usual trade-offs apply (shared content folder you must clear between downloads — the rename-or-lose-it dance), which -dir simply doesn't have:

> .\DepotDownloader.exe -app 264710 -depot 264712 -manifest 8427274798903478123 \
    -username you -remember-password -dir .\subnautica-aug2025

For the other eras, swap in the manifest matching the date from SteamDB's depot list. Each era is a modest full-game download, small enough to shelve several.

03SNAppData and the clean swap

Saves live inside the install Subnautica keeps saves in SNAppData inside the game folder — closer to KSP's portable anatomy than to the AppData crowd. That makes the community's swap procedure precise: replacing a build in place means delete everything except SNAppData, then put the downloaded era's files in. Never lay a new build over an old one's files — the half-merged result is the endless-loading-screen bug the guides all warn about, and the mistake I made the first time I swapped eras without clearing the folder. Back SNAppData up before any era move regardless (saves don't promise to travel between eras), set updates to "only when I launch", and the read-only-acf trick covers the rest. Side-by-side folders skip the whole ceremony, saves included.

04The Unity patch, second sighting

If you've read our Sons of the Forest guide, this is the same event from another shore: the 2025 Unity-runtime vulnerability forced patches across thousands of games, and in Subnautica's case the fix broke the BepInEx mod layer — so the modding community's standard advice became "revert to August 12 and wait." That's a legitimate, widespread move, and the manifest above is exactly that revert. The same honesty applies here as there: the pre-patch build carries the documented vulnerability the patch exists to close, and the developers' security argument for restricting old versions is the same coin's other face. Risk profile for an offline single-player diving game: modest. The right posture: revert knowingly, keep pinned builds for playing rather than as daily defaults, and when your mod stack crosses to the patched build, cross with it. Security patches remain the one update category this site won't talk you out of — even while documenting the revert.

05Mod stacks per era

Each era has its own plumbing, and they don't mix. Legacy runs the classic stack — QModManager plus SMLHelper — with the era-archaeology that implies: mods and their dependencies from Nexus old-files tabs, version-matched by trial where the dates run close (the community's documented pain, not laziness in this text). 2.0 runs BepInEx for Subnautica, which is the familiar territory of half this series — and for a pinned August 2025 build, era-correct mod versions per the usual discipline. The profile-transplant pattern transfers where managers support the game; the principle transfers everywhere: game build, loader, mods — one era, all three.

06Status in 2026

Subnautica's shelf situation is candid on every side: one official branch, openly bug-preserved; deeper history restricted with a stated security reason rather than silence; and a community that answers with maintained manifest tables and revert guides updated within weeks of each break. It's a near-opposite of another survival-exploration favourite, No Man's Sky, whose developer chose to archive the game's whole early history publicly — the gold standard a restricted shelf like this one isn't. The 2025 Unity event added something the series hadn't seen before — a current-era pin that exists for security-patch reasons, making the "revert knowingly" conversation mainstream here. The standing rules hold: manifests answer at Valve's pleasure, the one branch is the only officially promised past, and the era your mods live in is yours to keep — a folder per era, SNAppData backed up, eyes open about which build carries what. If it were my install, I'd grab the August 2025 build now and shelve it before that manifest goes quiet.