A server tells you what it plays: the launcher installs its pack and offers what it recommends — Keystone in its version, mods and its resource pack.

A server with Keystone says what it plays (pack, version, loader, Java, memory). After typing the address in Add server, in the server's detail or from a Play link without a pack, the launcher offers Install the server's pack — into the server's own instance with the right version, loader, Java and memory. Your instances are not touched; when the server moves to another version, only its instance is updated.
Downloads come only from CurseForge and Modrinth, by id and hash; nothing the server sends is ever run. A server's mod list is fetched only from public https addresses and its fingerprint must match.

Before you join a server (Play button, a link, the server list) and after a game in which you joined from the multiplayer menu, the launcher shows one panel with what the server recommends for your pack:
- Keystone's client part in exactly the version the server runs — if you have another version, the server's is added and yours is switched off; an older version than yours is never added unless you tick it.
- Mods the server recommends, with its reason in your language and their required dependencies.
- The server's resource pack ahead of time — downloaded, checked and switched on in the instance, so joining downloads nothing and textures do not reload.
- The memory the server recommends, when the instance starts with less — never more than your computer can carry (4 GB always stay free).
Everything is ticked except an older version; Add and play / Not now / Never for this server. Turn it off in Settings → Game → Servers.
A Keystone release the portals have not approved yet (a new release waiting for review) comes from Keystone's own update server — the same file, checked against the release's SHA-256. CurseForge and Modrinth still come first.
CurseForge comes first, Modrinth second (a switch in Settings → Game).

The benchmark on big packs (e.g. Create: Ultimate Selection 2, 384 mods) no longer ends with "The test took too long": the launcher waits as long as the game is really loading and gives up on the scene only when it stands still for 10 minutes. Switching to another window no longer pauses the game (the run is only marked invalid and finishes). When a test does not finish, the window says why (the game did not load / the scene stood still), the game log stays in logs/bench-failed.log, and Try again is one button.
The server's resource pack sits on top in a fresh instance and the pack's own resource packs stay switched on (a default options.txt of the pack could overwrite them before).
Before joining a server the launcher no longer asks whether to measure the pack; the benchmark no longer fails when the system keychain does not answer.
A narrow window (e.g. half the screen in a tiling window manager) no longer shifts clicks away from the buttons — the window may shrink to 560 px.
On a computer with no audio device (Linux without PipeWire/Pulse) clicks no longer send an error report.
A sign-in Microsoft refuses is no longer reported as a launcher error.

STYGION Launcher s0.12.0: what's new