They Are Billions: Survival Guide

How to survive the swarm in They Are Billions: the first ten minutes, economy rules, defensive layouts, unit choices, the final wave, and tips for the New Empire campaign.

Researched September 2026 — current as of the stable 1.1-era PC build (level editor rules update, November 2020); the game launched on Nintendo Switch 2 on January 22, 2026 but the PC game is not receiving new content. Mechanics below are stable.

Quick Start

• Pause constantly. They Are Billions is real-time with pause. Hit Space the moment the map loads and whenever something goes wrong. Planning while paused is the intended way to play.
• One leak kills a colony. Every building an infected touches becomes infected and spawns more zombies. Defend in depth and react instantly to breaches.
• Rangers first. They're cheap, fast, and quiet. Use them to clear the scattered infected around your base early.
• Noise attracts the infected. Soldiers, Snipers, and many buildings make noise; Rangers are quiet. Loud fights pull more zombies.
• Expand fast, but only behind defenses. The economy snowballs with space; unprotected expansions become infection sources.
• Walls plus towers plus units. Walls buy time, towers kill, units plug holes. None is enough alone.
• Watch the wave timer. The top-left shows when the next horde arrives and from which direction. The final wave on the last day is the real test.
• Survival saves are ironman-style. You can save and quit, but you can't reload to undo a mistake. Play carefully.

Resources and Economy

Resource | Produced by | Used for

Gold | Housing (colonists pay taxes), Market, Bank | Almost everything

Food | Hunter Cottage, Fisherman Cottage, Farm | Supports colonists and units

Workers | Colonists from housing | Staffing buildings

Energy | Tesla Towers distribute; Mill and Power Plant produce | Powers buildings

Wood | Sawmill | Buildings, walls

Stone | Quarry | Better buildings, stone walls

Iron | Quarry placed on iron deposits (later tech adds more options) | Advanced buildings and units

Oil | Oil Platform | Top-tier units and buildings

Rules of thumb:

• Housing is your gold engine. Tents early, upgrade to Cottages and then Stone Houses when you have the resources and tech.
• Food is the usual bottleneck. Place Hunter Cottages in forest areas without overlapping hunting zones; Fisherman Cottages on water; Farms on open meadow once researched.
• Sawmills and Quarries gain efficiency from covering more of their resource tiles. Hover to check the yield before placing.
• Tesla Tower coverage decides where you can build. Plan power lines toward your next expansion.
• Market and Bank turn the late game around: the Market increases gold income from nearby houses; the Bank multiplies it further.

The First Ten Minutes (Survival)

• Pause. Scan the map for resources near the Command Center: forest, stone, and iron.
• Build 2–3 Tents adjacent to the Command Center.
• Hunter Cottage in forest with plenty of green grid tiles showing game.
• Sawmill in dense forest and a Tesla Tower to extend power.
• Train Rangers (a couple at a time) from the start and send them out in small groups to kill nearby lone infected. Clearing the surroundings early is the difference between an easy and a hard mid-game.
• Quarry on stone as soon as you have wood income, then a Mill for energy.
• Wood Workshop to unlock research (and later the Stone Workshop).
• First wall line at the natural chokepoints facing the first wave's direction, with a Wooden Tower or two behind it.

Mid-Game Priorities

Once the first waves are handled and your base has a wall, the mid-game is about scaling safely:

Priority | Why

Stone Workshop research | Stone walls, better towers, and Stone Houses

Upgrade Tents to Cottages | More gold and workers per tile

Iron supply (Quarries on iron deposits) | Needed for Soldiers, Snipers, and advanced buildings

Market near dense housing | Big gold boost from nearby houses

Second and third food sources | Growth stalls without food; Farms need open meadow

Unit research | Unlocks Snipers and stronger units beyond Rangers and Soldiers

Radar or watch coverage | See waves early and pre-position units

Oil Platform (late) | Required for top-tier units like Titans

A useful habit: every time a wave ends, pause and ask three questions. Where did it hit? Did anything get through? What will the next, bigger wave need? Fix the answer before you invest in anything else.

Expansion checklist

• Clear the area with a group of units (not just Rangers once the infected get thicker).
• Extend Tesla coverage.
• Wall the new perimeter before placing houses there.
• Move towers and traps to the new outer line; keep the old wall as a second layer if it's cheap to maintain.

Defense Layout

A standard layered defense:

• Stakes or Traps in front (slow and damage the swarm).
• Two layers of walls, preferably stone once researched.
• Towers directly behind the walls (Wooden/Stone Towers early, Ballistas, Shocking Towers, and the Executor machine-gun tower later).
• Units parked behind the towers as a mobile reserve.
• Radar Tower or watchtowers to see incoming hordes early.

Tips:

• Use terrain chokepoints. Mountains, cliffs, and water are free walls.
• Leave space between walls and houses. A breach shouldn't instantly reach your economy.
• Don't wall everything at once. Cover the directions waves come from first; the final wave comes from multiple directions.
• Upgrade gates and walls before the late waves; wooden walls melt against big hordes.

Units

Unit | Role | Notes

Ranger | Early clearing, scouting | Quiet, fast, cheap; weak against crowds

Soldier | Mid-game line holding | Loud, sturdy, good sustained damage

Sniper | Long-range picks | Great behind walls and for special infected

Lucifer | Flamethrower, area damage | Excellent against dense crowds, short range

Thanatos | Rocket launcher, splash | Late-game crowd clearing

Titan | Heavy mech | Huge firepower, expensive, needs oil

Mutant (Survival) | Late-game melee brute | Research-gated; check its in-game tooltip for cost and upkeep

Composition: Rangers early for clearing, Soldiers/Snipers to hold lines mid-game, then Lucifers and Thanatos behind walls for waves, and Titans for the final wave.

Infected Types to Know

• Common infected: weak alone, deadly in crowds. Some variants are much faster than others and will outrun Rangers.
• Harpies: leap over walls; make sure towers and units cover the space behind your walls, not just in front.
• Venoms: attack from range; target them first.
• Giants: huge damage to walls; focus with Snipers and heavy towers.

Hover over any infected (paused) to check its type before deciding where to send units.

The Final Wave

In Survival, the last day brings the biggest horde from multiple directions at once. Prepare by:

• Upgrading all outer walls to stone (double layered).
• Stacking towers where waves converge (Executors and Shocking Towers are strong).
• Keeping a mobile army ready to plug any breach.
• Placing extra traps and stakes on approach routes.
• Pausing constantly during the wave to redirect units.

Survival Settings

You choose the map type, duration (days), and infected population before starting. Longer games and more infected raise the score multiplier but also the difficulty. Start on a shorter game with fewer infected and a gentler map (Dark Moor is the usual first), then move to Peaceful Lowlands, Frozen Highlands, Desolate Wasteland, and Caustic Lands.

The New Empire Campaign

• 48 missions and over 60 hours per the store page, led by Quintus Crane of the New Empire.
• Research tree with 90+ technologies; spend research points earned from missions.
• Hero missions send your Hero to explore ancient fortresses with no base building.
• Tactical missions focus on armies, not colony building.
• Campaign missions often allow more mistakes than Survival, but difficulty settings still bite; start on a lower difficulty if you're new.

Common Mistakes to Avoid

• Not pausing. The game is designed around it.
• Overbuilding houses without food. Colonists need food; shortages stop growth.
• Leaving lone infected near your base. They wander in and start chain infections.
• Building walls too close to houses. A breached wall becomes a breached colony.
• Sending Rangers into big crowds. They're scouts, not tanks.
• Ignoring Harpies and Venoms. They bypass or outrange naive defenses.
• Using loud units near quiet villages. You'll pull the whole village's infected onto you.

Advanced Tips

• Clear abandoned villages carefully for resources and loot. Draw infected out in small groups with a few Rangers and fall back to a defensive line.
• Expand in rings: secure a zone, wall it, then push the next ring.
• Snipers kill priority targets such as Venoms and Giants before they reach walls.
• Keep extra gold for emergency walls and towers during a wave.
• Upgrade economic buildings early: better houses and Markets pay for themselves quickly.
• Custom levels: the level editor (updated in v1.1 to allow rules modding) has a large Steam Workshop library for new challenges.

FAQ

Can I save and reload in Survival? You can save and quit, but you can't reload to undo mistakes; it's ironman-style.

What's the best early unit? Rangers, for cheap, quiet clearing.

How do I stop infections spreading? Kill the infected immediately; they turn buildings they touch. Keep units in reserve to respond.

Is there a sequel or new content? The PC game is complete; the most recent news was the Nintendo Switch 2 release on January 22, 2026, which supports Joy-Con 2 mouse mode.

Which map should I start on? Dark Moor with low infected population and a short game.

Is the campaign included? Yes, The New Empire campaign is part of the full game.

Sources

• They Are Billions on Steam
• Steam news: Switch 2 release (Jan 22, 2026), Modding Game Rules v1.1 (Nov 2020), v1.0.8 notes