KSP: one folder, one universe

KSP stopped updating in 2023 — 1.12.5 was the final patch, and after the sequel's collapse, KSP1 went from "the old one" back to being the one. So why does a finished game need old versions? Because its mod ecosystem never lived on a single version to begin with. A decade of development scattered the catalog across majors: most of the modern ecosystem calls 1.12.x home, but plenty of beloved mods and the big interconnected packs settled on earlier majors and stayed — when a pack's documentation names a version, it means it, to the digit. Add save-compat caution for decade-old careers, the odd nostalgia run, and modders testing across eras, and "which KSP" remains a live question years after the last patch.

01The portable anatomy

Here's what makes KSP the easiest version-keeping on this site: the install folder is the whole world. Saves (saves/), craft files, mods (GameData/), config — everything lives inside the game directory; there's no AppData annex, no cloud entanglement to fight, no wrapper DRM on the executable. Copy the folder anywhere and double-click KSP_x64.exe; it runs. The community has worked this way forever — a "career install", a "testing install", an "RP-1 install" — which means this game's version of the archiving gospel is one sentence: a copied folder is a complete, launchable universe, saves and mods included. Every other game here needs a three-part backup checklist; KSP needs Ctrl+C.

02The branch shelf, back to 1.0

Steam's Betas tab on KSP carries an unusually deep dropdown — builds reaching back to 1.0 (2015), generally the settled patch of each major. Anything older than 1.0 predates the shelf entirely and isn't on Steam in any form. Branch switching swaps your Steam install as usual; the more KSP-native move is pulling a branch into its own folder, where it joins the portable-install collection:

One hygiene rule the forums repeat for in-place downgrades: never downgrade a dirty install. Leftover newer files in GameData (including the stock Squad folders) confuse older builds — which is one more argument for the fresh-folder way of life. This is exactly what bit me the one time I downgraded in place instead of into a clean folder, and I haven't done it the lazy way since. If you own the DLCs (Making History, Breaking Ground), note they're era-versioned too: their content installs into GameData/SquadExpansion, and an old game build wants the DLC files that shipped for it, not today's.

03Unlisted versions by manifest

The dropdown is deep but not exhaustive — point releases between the listed builds follow the standard route: release date from the KSP wiki's version history, matched manifest from your platform's depot on SteamDB's app 220200 page, then -manifest per the universal guide. The game is a few gigabytes; a complete shelf of every major you care about fits on any drive. And because the catalog is finished, this is shopping with a fixed list — there will never be another KSP1 version to chase.

04CKAN keeps the eras straight

Mod-era bookkeeping — the chore every guide in this series assigns to discipline — is, in KSP land, somebody's solved problem. CKAN, the community's mod manager, thinks in instances: File → Manage Game Instances, point it at each of your folders, and it tracks every install separately — resolving, for each one, only mod releases compatible with that instance's game version, pulling old mod versions from its metadata-tracked archives. It's the r2modman-profile-transplant pattern from the BepInEx games with the transplant step designed out. Workflow for a pinned era: download the folder, register it in CKAN, set the compatible-versions filter, install the pack. The era stays coherent because the tooling refuses to let it drift.

05Status in 2026

KSP gives this series something no other page has: an endpoint. Every other status section warns that today's current build is tomorrow's old one; KSP's history stopped moving in 2023, so the collection can actually be finished — the branches are live and deep, the depot history is bounded, and a few tens of gigabytes archives the entire lineage of one of PC gaming's great modding platforms. The asterisks are the standing ones: branches and manifests are served at Valve's pleasure (the weather page applies to finished games too — arguably more, as their request traffic fades), and pre-1.0 history was never on Steam at all. The move writes itself: complete the collection while the shelf is fully stocked. It's the rare archive with a last page, and you can own all of it. On my last check, June 2026, every branch I wanted was still pulling fine — but that's exactly the kind of thing I wouldn't bet on staying true, so I grabbed my majors while they were there.