Duo Rust servers

It is a server whose published group limit is set to 2, so the game stops you forming a team larger than that. The limit is chosen by the owner and enforced in game. This page lists servers by that setting, whatever their name says.

Check the Group column here rather than the title. A server can call itself duo and still publish a higher limit. We read the published setting at each refresh, and any server that moves off 2 drops out at the next scan.

That is up to each owner. The map resets at the monthly force wipe for everyone, but blueprints may reset monthly, on a different cycle, or not at all. The server's own page or Discord is the place to confirm before you start.

There is no fixed answer. Some run 2x, some run vanilla 1x and leave it out of the name, and others go higher. Where the owner publishes a rate, the Tags column shows it, so use that to match a server to the pace you want.