The IRON NEST multiplayer mod: five-player co-op

IRON NEST has no official multiplayer, but a mod on Nexus adds co-op for up to five players over Steam. It is the only way to crew a nest with other people today, and it works better than a bolted-on mode has any right to.

Does it work on the current patch?

This is the question that actually decides whether your session happens, because game patches break the mod faster than most pages get updated. Current status:

The release month set the pace: the mod shipped its full-release update on launch day, and a game build later that month broke the then-current version outright, with the fix arriving about four days later. Assume any game patch can do this again. Before a session, check the author's GitHub releases feed for a build-compatibility note — fixes land there first — and make sure the whole crew updates together.

What the mod actually does

The mod splits the operator's job across a crew. Instead of one person reading orders, plotting targets, choosing charges, loading shells and firing, each of those stations can be held by a different player — manning the guns, loading shells, and working the artillery computer as separate roles.

Connection is peer-to-peer over Steam, no separate server or account. One player hosts and creates a lobby, which generates a short join code; everyone else types that code in and joins. Firing is host-authoritative: the host distributes the exact firing values — angle, elevation, charge, shell — so impacts are identical for every player.

What stays in sync is most of what matters: mission loading and progression, turret aiming, station actions (magazines, shells, powder charges), the fire-mission cards the artillery computer generates, map-table drawings, supply-console ammunition and repositioning, and player avatars with name tags. Two things are deliberately not synced: music, and the artillery computer's input fields — only the generated cards replicate, so each player can work their own numbers.

This is why it works as well as it does. The single-player game already separates the stations physically inside the nest; you simply move between them. The mod does not invent a co-op mode so much as let more than one pair of hands occupy a design that was already built around distinct posts.

Install the loader first

This is the step that stops most first attempts, and the failure is silent. The co-op mod runs on BepInEx 6 — specifically the IL2CPP, 64-bit bleeding-edge build (6.0.0-be.785 at the time of checking). BepInEx 5 does not work: it only supports Mono games, and IRON NEST is IL2CPP. A correctly placed mod without the right loader simply does nothing — no error, no warning, no message explaining why.

Two install routes, from the mod's own instructions:

• Standalone package — copy the entire package into the game folder, so winhttp.dll and the BepInEx folder sit next to the game executable. The first launch takes several minutes while BepInEx initializes; that delay is normal, not a hang.
• DLL-only — if you already run BepInEx 6 IL2CPP for other mods, drop IronNestCoop.Core.dll into BepInEx\plugins\.

MelonLoader, the other loader you will see mentioned around IRON NEST modding, is used by other mods — it is not a substitute here. Installing the wrong loader produces exactly the same silent nothing as installing none.

Everyone needs the same setup

Co-op mods are version-sensitive in a way single-player mods are not. Every player must run the identical mod version, on the same loader — a mismatch between crew members typically shows up as a connection that fails or a session that desyncs rather than as a clear error message.

Agree on versions before a session rather than during one. If the game has patched recently, check the status table above and the releases feed before everyone updates.

Drop-ins, reconnects and other limits

Known limits worth planning a session around:

• No mid-mission drop-in. A player who was not there when the mission started cannot join it partway through.
• Reconnects are for the original crew only, and best-effort. A player who disconnects can rejoin and resync — chambered shells and staged propellant are re-established — but complete state restoration is not guaranteed.
• Briefing text follows the host's language. The typewriter texts from High Command and Field Reports are sent by the host, so a mixed-language crew all reads them in the host's language.
• Closed source. The mod is licensed CC BY-NC-ND and the code is not published; the author's GitHub repository serves as the issue tracker and release feed.

The alternatives: Synchrony and the VR bundle

Two other Nexus entries overlap with this one. Synchrony is an independent co-op mod that appeared after launch, with its own approach: hosting from an in-game "Play Multiplayer" button with an invite code, and syncing turret aim, gun fire and reloading, mission and objective progress, requisition, map entities, and even valves, lamps and hatches. It is younger and less battle-tested than the main co-op mod, and the two are separate projects — a crew must all run the same one.

An older entry bundles VR, co-op and PvP intentions together. Its scope is wider and less settled than either dedicated co-op mod, so treat it as more experimental. If your goal is simply to play with friends, the main co-op mod remains the most-used answer.

How this relates to official co-op

There is no official multiplayer in IRON NEST, and none is planned for this title. The developers' replies on the Steam boards are consistent: this game is single-player by design, and official co-op is the core of their next game — a separate, fully multiplayer title targeting around 2027, funded by what this one earns. The multiplayer guide on this site covers those statements in full.

The practical reading: if you want to play IRON NEST with someone this month, the mod is the route. Do not buy the game on the expectation that official co-op is arriving.

What using it costs you

Mods here are unofficial and unsupported. The status table at the top shows how quickly a game patch can take a working version down, and stability is whatever the author achieved rather than what the game guarantees.

Whether medals and Steam achievements record normally in a modded session is unconfirmed — no verified information exists here. Note that these are two separate systems: IRON NEST has over a hundred in-game medals and 33 Steam achievements, so a mod could plausibly affect one and leave the other intact. If you are working toward either list, finish that first and mod afterwards.

Whether the co-op mod supports the free demo build rather than the full game is also unconfirmed.

Installing without breaking things

Back up your save before the first mod goes in. This costs nothing and is the difference between an experiment and a gamble, since reverting a modded save to a clean state is not something this site has verified as reliable.

Install one mod at a time and launch the game between each. When something breaks — and with co-op mods across five machines, something eventually will — you want to know which addition caused it rather than guessing across a stack.

Read the mod page's own instructions rather than a general modding tutorial. Loaders place files in different locations, and generic guidance is where most mismatched installs come from.

Where to get it and get help

Nexus Mods hosts the IRON NEST mod scene, and the co-op mod's page carries the download. The author's GitHub releases feed is where compatibility fixes appear first after a game patch — both of the release month's fixes landed there before anywhere else — and its issue tracker is where breakage gets reported and confirmed.

The official Discord has mod channels where authors post directly and answer installation questions. For loader problems specifically — the single most common sticking point — asking there resolves things faster than working through comment threads on a mod page.

Download counts change constantly, so this page does not quote them. Version numbers live only in the dated status table at the top, which is re-checked on this site's regular schedule.