SAS: Zombie Assault 4: Complete Guide

A player's guide to Ninja Kiwi's free-to-play co-op shooter SAS: Zombie Assault 4: classes and skill trees, every map and its objective, zombie types, loot and augmentation, co-op tactics and how the community events work, plus where the successor stands.

Researched September 2026 — current as of the live Steam build and the 2025 community events (Kurios, Saon rift and weapons-cache transmissions). Live games change; check the linked sources if something differs.

Status note: SAS4 is still free on Steam and still runs community events, but Ninja Kiwi's development focus has moved to its successor, Zombie Assault: Resurgence, which had public playtests in 2024-2025 and a Steam Next Fest demo in February 2026. Resurgence is a separate game; your SAS4 progress stays in SAS4.

Quick Start

It is free to play. Everything important drops from play; in-app purchases exist but are not required to progress.
Pick a class: Assault, Medic or Heavy Gunner. Each has its own 19-skill tree. You have multiple character slots, so you can level all three.
Your loadout is a pistol plus two rifle-class weapons, armour, turrets, grenades and special ammo.
Open every strongbox. Guns and armour come from strongboxes found in secret rooms and dropped by zombies. Higher-level play means rarer boxes.
Augment your best gear. Augmentations add damage, rate of fire, reload speed or resistances. Keep upgrading the same favourite pieces.
Armour resistances matter. Zombies deal physical, thermal and chemical damage; build resistance to what is killing you.
Play co-op. Quickmatch pairs you with up to three players of similar level; mixed classes clear much faster.
Learn the maps' objectives. Each of the seven story maps has a different victory condition; winning is about the objective, not just kills.
Hunt hidden stashes. Every original map has secret rooms with extra loot ("You Have No Secrets" for finding them all).

Classes and Key Skills

Class	Role	Notes
Assault	All-round damage dealer	Flexible weapons; strong solo and in groups
Medic	Support and survivability	Has the Biocleanse Bomb, which slows zombies
Heavy Gunner	Tank and sustained fire	Built for heavy weapons and soaking damage

The store highlights three high-level room-clearing powers: Assault Team, Aerial Bombardment and Zombie Antidote (which "heals" zombies to death). Other skills named in the game include Fast Reload, Fast Movement, Toughness, Body Armor, Health Regen, Energy Regen, Close Quarters Combat (melee bashing) and Die Another Day (resisting zombie attacks). Check each class's tree in-game to see which it gets.

Skill point rules of thumb:

Early levels: put points into survivability (Toughness, Body Armor) and one damage or utility skill that defines the class.
Fast Reload and Fast Movement are strong on every class.
Energy Regen powers your active abilities; invest once you rely on them.
Community skill-build guides on Steam go deeper; the top-rated one breaks builds down by class.

Maps and Objectives

The original seven story maps each have a different win condition, plus the later Recovery map:

Map	Objective	Achievement hook
Pods	Destroy zombie pods (the boss pod ends it)	"Precision": open no pods besides the boss pod
Last Stand	Hold barriers against waves	"NLL": no zombie gets through; "Hard Line": none past the first barrier
Onslaught	Defend the ship's ramp	"None Shall Pass": ramp doors never fall
Power Out	Complete the map's power objective (turrets are part of the threat)	"Zero Casualties": no 4-player team member takes turret damage
Survivors	Rescue survivors	"Hero": rescue every survivor
Vaccine	Extract the vaccine to the ship	"Team Sprint": 4 players, extract and board in under 5 minutes
VIP	Escort the VIP out	"Transporter": VIP takes no damage; "Redecorator": break everything in his mansion
Recovery	Later map with vehicles	"Eco Warrior": complete without entering a vehicle

Vehicles appear on some maps. Ramming zombies is effective (and has several achievements), and you can even crush a boss.

Zombie Types

SAS4 has 17 zombie types that can evolve new powers as you progress, plus bosses. Named types from the game's achievement list include:

Zombie	What to know
Shamblers	The common zombie; the bulk of every horde
Runners	Fast movers; prioritise them before they close the gap
Stalkers	Common enough to have their own 5,000-kill achievement; keep your flanks covered
Spitters	Ranged attackers; keep resistances balanced
Bloaters	Heavier zombies; do not let them reach you in a crowd
Shielders	Built to absorb fire; burst damage and explosives help
Wickers	Their achievement is "extinguishing" them, so expect fire
Devastators	Tough elite-tier threats; focus fire
Zombie Mechs	Armoured threats; bring high damage
Regurgitators	Boss type that pukes out acid worms
Necrosis	Boss type that comes with three children, which also need killing

Bosses can enter a rage mode and hunt you down; keep moving, and let turrets and teammates share the aggro.

Loot, Strongboxes and Augmentation

Over 160 guns and armour pieces drop from strongboxes of increasing rarity.
Grades: each item has a grade, and at high levels you can find powerful RED versions.
Black strongboxes and Black Keys are the high-end loot tier; the community has dedicated guides on how to earn Black Keys through play.
Weapon types: SMGs, shotguns, assault rifles, machine guns, flamethrowers, rocket launchers, lightning guns and more.
Augmentation: add augments to guns and armour, then raise each slot's grade (grade 5 and grade 10 are milestones). Focus augment materials on a small set of items you will use for a long time.
Selling: sell unwanted weapons and gear rather than hoarding them (5,000 sold is "Recycler").
Cash: SAS4 Cash drops from zombies; it pays for upgrades.

Loadout tips:

Carry one crowd weapon (SMG, machine gun, flamethrower) and one burst weapon (shotgun, rocket launcher) plus a pistol for emergencies.
Match damage types to your team; flame is great against hordes, but resistances differ by zombie.
Turrets carry low-level co-op; place them at chokepoints before waves.

Co-op Tactics

Split roles: Assault on damage, Medic on sustain and slowing, Heavy Gunners holding the line.
Stagger big abilities (Assault Team, Aerial Bombardment, Zombie Antidote, Biocleanse Bomb) instead of popping them together.
Move physics objects to build temporary cover and funnels.
Coordinate turret placements so they cover different angles.
Revive fast and don't wander into unexplored rooms alone; Stalkers punish it.

Events and Community Goals

Ninja Kiwi runs story-driven community events through Steam announcements, usually framed as transmissions from the SAS or USI. Recent ones in 2025 included the push to take back Thrace and Kurios station, a rift opening on Saon with a giant monster and zombies pouring out (October 2025), and a hunt for a hidden government weapons cache (December 2025). The pattern is the same each time: everyone's zombie kills count toward global milestones, and players are rewarded when milestones are hit. Just playing normally during an event contributes.

The store also lists PvP events such as Last Man Standing.

Levelling Plan

Levels 1-10: learn the maps on easy settings; unlock core skills. Level 2 and 11 are early achievements.
Level up all three classes to 10 ("Test Driven") if you want to try everything.
Levels 10-50: move to harder settings as your gear allows; start augmenting your favourite weapon.
Level 50+: chase rarer strongboxes and RED gear; push augment grades toward 10.
Endgame: Black strongboxes, high-grade augments and community events.

Common Mistakes to Avoid

Ignoring armour resistances. Physical, thermal and chemical damage all matter.
Spreading augments across too many items. Pick favourites and max them.
Running into unexplored rooms alone. Ambushes and Stalkers punish it.
Focusing kills over objectives. Survivors die, the VIP dies, ramps fall.
Wasting ultimate-style abilities on small packs. Save them for hordes and bosses.
Buying things before learning the game. Almost everything drops from play.

Advanced Tips

Car explosions kill packs; lure zombies near cars and detonate them (5+ kills in one blast is "Impounded").
Drift in vehicles to flatten crowds (20 in one drift is "Drift King").
Grenades and special ammo are underused; they carry you through bosses.
Die Another Day plus Body Armor and Toughness makes a forgiving build for harder settings.
Farm your favourite map for the "Map Master" counters (1,000 completions each) if you are going for 100%.
Keep an eye on Resurgence. If you enjoy SAS4's loop, the successor's demo features three Merc classes (Assault, Heavy, Medic), maps like the Mining Facility, Abandoned Colony and Icefield, and bosses including the Regurgitator and Shredder.

FAQ

Is SAS: Zombie Assault 4 free? Yes, it is free to play on Steam with optional in-app purchases.

Is SAS4 still being updated? It still runs community events and remains online, but new development is focused on Zombie Assault: Resurgence.

Which class is best for solo? Heavy Gunner or a survivability-focused Assault; Medic shines most in co-op but its self-sustain is solid.

How many maps are there? Seven story maps in the original release (Pods, Last Stand, Onslaught, Power Out, Survivors, Vaccine and VIP) plus Recovery added later.

How do I get better loot? Level up, play harder settings and open more strongboxes. Black Keys and Black strongboxes are the top tier.

Does my progress carry over to Resurgence? No official carry-over has been announced; treat them as separate games.