IRON NEST 1.0 ships as a single-player game. There is no official multiplayer, no co-op and no PvP in the release build. If you are buying it to crew a gun with a friend, buy it knowing that.
What the developers have said
The developers have discussed multiplayer publicly, and this is where most of the confusion around this question comes from. A developer reply on the Steam boards, marked as the answer to a co-op question, states that official co-op is planned for the next IRON NEST game rather than this one — the first game is single-player, and work on proper co-op begins after it.
Alongside that, the pair have described a long-term plan in which a second title would be fully multiplayer, with co-op as the core and PvP or PvPvE still under discussion internally.
The conflict you should know about
Not every source agrees with the reading above. Some secondary write-ups describe co-op missions and competitive modes as planned for the base game, arriving post-launch alongside additional missions and an expansion.
These two accounts cannot both be right, and this site has not resolved them against a primary source. Unconfirmed — treat any claim that co-op is coming to this game as unconfirmed until you have read it in the official FAQ or a developer post yourself. This matters more than most open questions on this site, because it is a purchase decision rather than a tactical one.
The safest position: buy IRON NEST for what it is today, which is a single-player campaign that reviews extremely well. Do not buy it on the expectation of co-op arriving.
The unofficial co-op mod
The community solved this without waiting. A mod on Nexus adds multiplayer for up to five players over Steam, letting a crew split the work — manning the guns, loading shells, and working the artillery computer as separate jobs rather than one operator doing everything.
This is arguably the most interesting thing about IRON NEST's multiplayer situation. The single-player loop already divides cleanly into stations, so distributing those stations across real people does not require redesigning the game; it requires networking what is already there.
A second mod bundles VR, co-op and PvP intentions together, though its scope is broader and less settled than the dedicated co-op mod.
What you need before installing
Mods for IRON NEST run on a loader, and this is the step that stops most first-time installs. You need either BepInEx Bleeding Edge or MelonLoader installed first — both provide the IL2CPP support that the actual mods depend on.
Installing the co-op mod without a loader present will simply do nothing, with no error explaining why. Check which loader the mod page specifies before downloading anything else.
Expectations for a modded crew
Treat unofficial multiplayer as unofficial. It is not supported by the developers, it can break with any game patch, and stability is whatever the mod author has managed rather than whatever the game guarantees. Medal and achievement behaviour in a modded co-op session is unconfirmed — no verified information exists here on whether progression records normally.
If you want to try it before buying, note that the free demo runs the same fire-control loop. Whether the co-op mod supports the demo build specifically is unconfirmed.
The short answer by use case
If you want to play with a friend today, the mod is the only route, and it works well enough that people use it. If you want an officially supported co-op campaign, nothing announced covers this game with confidence — the clearest developer statement points at a separate future title.
If you are simply asking whether the game is worth playing alone: it was built as a single-player experience, and its reviews reflect that rather than being an apology for a missing mode.
Where to check for changes
The Steam discussion threads on co-op and multiplayer carry the developer replies directly, which makes them the primary source rather than a summary of one. The official Discord is where roadmap changes surface first. If official multiplayer is ever confirmed for this game, it will appear in one of those two places before it appears on any wiki.