What this covers: The 2.1 update’s circuit-network additions — pipes and pipelines, boilers, heat exchangers and heat pipes, labs, land mines and agricultural towers — plus the selector combinator’s new time, index and quality-select modes. Why it matters: These are devices a circuit signal could not previously read or steer directly, so a class of builds — fluid control, research routing, quality sorting — can now act on the measured quantity instead of a proxy. Who should care: Factorio players who already wire up inserters, tanks and pumps and want to know which old workarounds 2.1 makes redundant.
Factorio’s circuit network has always been a way to read a number off a machine and act on it. The 2.1 update widened both halves of that sentence. Wube Software released it to the experimental branch on 26 June 2026, and the game’s patch history dates the bulk of the circuit work to 2.1.7 on 23 June 2026. This is the systems guide: what the network can now see, what it can now control, and where the new selector-combinator modes fit.
What joined the circuit network
The clearest way to see the scale of the change is to list the devices that gained a wire connection and what each one can now report or receive. Every row below is drawn from the changelog for 2.1.7 unless the row says otherwise.
| Device | What it can now read | What the network can now set |
|---|---|---|
| Pipe / pipe to ground | Contents of the individual pipe or the whole pipeline, and the fluid’s current temperature | — |
| Boiler | Current fuel, including the fuel being burned | Enable/disable |
| Heat exchanger | — | Enable/disable |
| Heat pipe | Wire connection | — |
| Lab / Biolab | Contents, current technology cost, and technology level | Set the current research |
| Land mine | — | Explode on a condition, disabling proximity triggering |
| Agricultural tower | Seeds and harvested plants in its inventory | Planting and harvesting, separately |
| Requester and buffer chests | Contents | Requests — read and set at the same time |
The 2.1.7 notes also list storage-tank fluid volume scaling with quality, so a higher-rarity tank holds more of the fluid whose contents it already reported, and lab research cost and technology level as new readouts alongside the lab’s contents.
Pipes and pipelines: reading fluid where it sits
The pipe entry changes the most patterns, because it turns the fluid system into something you can measure at two resolutions. A connected pipe can report the contents of the individual pipe, or the contents of the entire pipeline it belongs to, and in both cases it can output the fluid’s current temperature. Underground pipes gained the same reads.
That distinction matters because of how the fluid system works since 2.0.7, when contiguous pipes and storage tanks were merged into segments: each segment contains a single fluid, and throughput is proportional to how full a segment is. “Read pipeline contents” is therefore a reading of the segment — the whole connected run — while “Read contents” is the one tile in front of you. If a pipeline spans several machines, the segment reading is the one that tells you the total, and the per-pipe reading tells you what is local to that connection.
Wube also changed how much of the fluid system is drawn on screen. Holding a fluid-related entity now shows pipeline visualisation only in alt mode, the automatic visualisation on hover was removed, and there is an interface setting to disable pipeline visualisation entirely, plus a checkbox and an unbound hotkey to persistently highlight the pipelines a given entity belongs to. The same release added fluid-mixing warnings: attempting to connect two pipes with different fluids raises a warning until the conflict is resolved.
Labs: reading research and setting it
A lab can now report its contents, its current technology cost and its technology level, and the network can set the current research from a condition. The wiki spells out the catch: if research is set this way, players are prevented from switching research on the technology tree by hand. Control handed to a circuit is control taken away from the tech tree, so a lab-driven research queue needs an explicit off switch — release the condition rather than fight the GUI.
Wube spent the experimental run patching the edges of this feature. 2.1.8 (25 June 2026) fixed labs that set research blocking a manual change while disconnected from the circuit network. 2.1.10 (13 July 2026) fixed the lab conditions GUI not live-updating the researched state while open. 2.1.17 (26 August 2026) fixed that setting research from a lab would not always mark the active research as set by lab behaviour. A feature this new with three targeted fixes is one worth re-testing against your own build rather than assuming the behaviour you saw in July still holds.
Boilers, heat exchangers and heat pipes
Boilers, heat exchangers and heat pipes all joined the network in the same release, but they do not do the same thing. A boiler can output its current fuel, including the fuel currently being burned, and it can be enabled on a condition. A heat exchanger can be enabled on a condition, but the circuit network’s device table lists no output signal for it. Heat pipes gained a connection with no listed read or control.
Two later fixes describe the failure modes worth watching for:
- 2.1.15 (24 August 2026): “Fixed that many machines with passthrough ports would continue to produce and consume fluid from overextended pipelines.”
- 2.1.22 (15 October 2026): “Fixed that heat-fluid-inside boilers would continue to work even if their input pipeline was overextended.”
Both are the same class of bug — a machine kept working past a pipeline limit — and both were fixed months apart, which is a reminder that a wired pipeline does not automatically respect the limits you set on a wired machine.
The selector combinator’s new modes
The selector combinator is the 2.0-era combinator for filtering and analysing signals; it sits alongside the constant, arithmetic and decider combinators. The wiki describes it as having five modes without Space Age enabled and nine with it, and 2.1 added two that matter to base-game players.
| Mode | What it does | Version |
|---|---|---|
| Select input | Sorts inputs by value and outputs one by a 0-based index; the index can carry a greater/less-than modifier to output a range | 2.0.7 |
| Count inputs | Counts unique input signals, ignoring their values | 2.0.7 |
| Random input | Passes a random input signal every N ticks (default: every tick) | 2.0.7 |
| Stack size | Outputs the stack size of input items, ignoring values | 2.0.7 |
| Time | Outputs game tick (T), day tick (D) and day length (L) virtual signals | 2.1.7 |
| Quality select | Passes the highest or lowest quality of each signal type, keeping its value | 2.1.21 |
| Rocket capacity | Outputs the rocket capacity of input signals | Space Age |
| Quality filter / transfer | Filters signals by quality, or attaches a chosen quality to a target signal | Space Age |
Time mode
Time mode outputs three virtual signals. Game tick, default signal T, counts up by one every tick starting when the world is created. Day tick, default D, counts up by one every tick and resets at the value of day length. Day length, default L, is the number of game ticks in a day on the current planet — the wiki gives 25,000 on Nauvis. That is a day/night clock you can wire without building a clock out of a feedback loop, and it is the kind of quantity players previously reconstructed from an accumulator’s charge percentage.
Index comparator
The 2.1.21 changelog adds an “index comparator” to the selector combinator, which it describes as allowing selection of the N highest or N lowest signals. The selector page folds this into select-input mode: the index picks a position in the sorted list starting at 0, and a greater/less-than modifier turns a single pick into a range above or below it. Two edge rules matter in practice. With multiple input signals, an out-of-bounds index passes no signal through. With a single input signal, that signal is always passed through even when the index is out of bounds.
Quality select
When several qualities of the same signal arrive, quality select passes through either the highest or the lowest quality of each signal type, and a passed signal keeps its value. The wiki notes it can include fluids and virtual signals — which do not normally carry quality — if a constant combinator is creating them. This mode had a short settling period: 2.1.21 fixed “quality selection flickering,” and 2.1.22 fixed the quality-select switch’s wrong initial state.
Channels, chests and splitters
Two long-standing rules frame all of the above. A circuit network carries a channel for every item plus 48 user-definable virtual signals, with the Everything, Anything and Each wildcards; unrelated wires do not merge, and each connected set of same-colour wires is its own network. Values are signed 32-bit integers in two’s complement, and they wrap on overflow — 2,147,483,647 plus 10 becomes −2,147,483,639. A counter that climbs unchecked will eventually fold over, and the wrap is silent.
Requester and buffer chests are the change to watch if you built a chest where one wire both set and read. 2.1.7 lets them set requests and read contents at the same time, retiring the old workaround that split the two jobs across a delay. The same release grouped a circuit-connectable entity’s settings into “Input” and “Output” sections and added the option to choose which wires — red, green or both — an entity uses for input, and separately for output.
Splitters have been circuit-connectable since 2.0.67 and behave in a way that catches people out. A splitter can set its priority input and output sides on a condition, and it can set its filter from a signal — but setting a filter only works if “set output sides” is enabled and the condition for either left or right is true. If both sides are true it filters to the left, and if several input signals could serve as the filter it chooses the item that appears first in the Factoriopedia.
What it changes in practice
The practical upshot is that a set of builds that used to read an indirect signal can now read the thing itself.
- Fluid control. Read a pipeline’s contents or its fluid temperature and enable a boiler or heat exchanger on that condition, rather than inferring fluid level from a storage tank somewhere upstream.
- Research routing. Set a lab’s research from a condition to queue a technology automatically — but remember that this locks manual selection until the condition is released.
- Day/night logic. Time mode’s T, D and L signals replace a hand-built clock for anything that cared about the tick, the time of day or the length of a day.
- Quality sorting. Quality select separates a mixed-quality signal stream into highest or lowest per signal type, which is a sorting step that previously needed several combinators.
- Prioritising. The index comparator answers “which N signals are largest” or “smallest,” so an alarm can target the most-depleted resource instead of an arbitrary one.
Where the network has to travel between surfaces, radar circuit connections gained a “universe” mode for transferring cross-surface signals in the same release. The broader space-logistics side of 2.1 — mixed rocket payloads, platform-to-platform transfers and circuit-controlled hub requests — is covered in Factorio 2.1 Mixed Rocket Payloads and Platform Cargo.
Running it on experimental
Wube’s own notes carry the caveats. The 2.1 experimental release post states that 2.0 save games will load but that there may be changes that break factory designs, that players should back up saves and blueprints, and that once updated, blueprints and save games cannot be downgraded to 2.0. Mods you rely on may not be updated yet. The same post raised the minimum Linux GLIBC to 2.36 and the minimum macOS to 10.13, while noting that the headless and Steam versions are not affected by the GLIBC change.
The plan post is equally plain about longevity: 2.1 is intended to be Factorio’s last major update, and Wube said it planned to leave 2.1 on the experimental branch over the summer so mod authors had time to catch up. As of 2.1.22 on 15 October 2026 the build is still experimental, and its changelog continues to land circuit fixes — the quality-select initial state, and the boiler pipeline overrun — rather than new circuit features. If you have a factory to protect, copy it before you switch branches.