Co-op and multiplayer guide

How co-op works

• Up to four players can play together online; one player hosts.
• Each world has a single dog, owned by the host. Guests may see only its harness moving instead of the dog.
• Guests can't join until the host has reached the cabin.

Source: Known Issues & Workarounds (updated October 11) · Official Co-op Guide

Joining a friend

• Steam invites work since the October 11 patch: the friend you invite must already be sitting in the game's main menu. The developers' pinned known-issues post, edited later that day, still lists invites as not working, so if an invite fails, join through the in-game server list instead.
• The in-game server list is the other way in. Since October 10 its friends-only view lists friends' worlds first and shows more servers.
• Authentication-token error, or multiplayer greyed out: take Steam out of offline mode and switch off any VPN.

Source: Quest Fixes & Steam Invites (October 11 patch notes) · Official Permafrost news · Known Issues & Workarounds (updated October 11)

See the patch notes for the full list of co-op fixes.

Quests in co-op

Most quest blockers so far happen in co-op or when steps are done out of order. The developers' advice:

• The host should be the one who advances the main story and Skinwalker's quests.
• The Way Home (Reach House Camp): only the host should open Skinwalker's box, also when two keys exist. In the developers' tests this worked every time, while a guest opening it broke the quest.
• Keep a copy of your .pfs world save before major quest steps; restore it only while the game is closed.

Source: Quest Issues & Workarounds

Missing quest key: since the October 11 patch Anna or Skinwalker replace it if it is in neither your inventory nor the reward chest.

Source: Quest Fixes & Steam Invites (October 11 patch notes)

More quest fixes: Fixes and known issues.