While there isn't a single official "SWAT 4 Zombie Mod" that dominates the community, the tactical realism of

is the spiritual successor to SWAT 4, it has a popular Zombie Or Not mod on Nexus Mods that replaces suspects with fast-attacking zombies. No More Room in Hell (NMRiH)

zm_hospital (creepy patient rooms and an underground morgue)
zm_warehouse (open spaces – terrible for shotguns)
zm_fairfax_night (all lights off, only gunfire and screams)

Custom zombie models – Decayed, bloody retextures of existing SWAT 4 characters, plus some imported from other Source engine games.
Horde AI – Zombies don’t use cover, don’t surrender, and never negotiate. They just walk toward you. But they do open doors, break glass, and follow sound.
Gradual infection – In some versions, getting meleed by a zombie triggers a poison effect. If untreated (by a teammate’s medkit within ~60 seconds), you turn into a zombie yourself – now controlled by AI, attacking your former squad.
No scoring for compliance – Forget the “Mission Score” system. The only stat that matters is survivors extracted.
New equipment – Some mods add molotov cocktails, barricade kits, and motion sensors. Others strip your gear down to just a pistol and a flashlight.

Swat 4 Zombie Mod Today

While there isn't a single official "SWAT 4 Zombie Mod" that dominates the community, the tactical realism of

is the spiritual successor to SWAT 4, it has a popular Zombie Or Not mod on Nexus Mods that replaces suspects with fast-attacking zombies. No More Room in Hell (NMRiH) swat 4 zombie mod

zm_hospital (creepy patient rooms and an underground morgue)
zm_warehouse (open spaces – terrible for shotguns)
zm_fairfax_night (all lights off, only gunfire and screams)

Custom zombie models – Decayed, bloody retextures of existing SWAT 4 characters, plus some imported from other Source engine games.
Horde AI – Zombies don’t use cover, don’t surrender, and never negotiate. They just walk toward you. But they do open doors, break glass, and follow sound.
Gradual infection – In some versions, getting meleed by a zombie triggers a poison effect. If untreated (by a teammate’s medkit within ~60 seconds), you turn into a zombie yourself – now controlled by AI, attacking your former squad.
No scoring for compliance – Forget the “Mission Score” system. The only stat that matters is survivors extracted.
New equipment – Some mods add molotov cocktails, barricade kits, and motion sensors. Others strip your gear down to just a pistol and a flashlight.