Survival VS is a mode exclusive to Killing Floor 2 that was added as part of the Revenge of the Zeds update. It is the first official PVP game mode in the Killing Floor series.
In this modes, two teams of up to six players each compete in two around. In the first round, one team plays the mercenaries while the other plays the zeds, and in the next round they switch. Then the scores are compared to determine the winner.
When playing as the mercenaries, the game works like a regular Survival Mode game. Survival VS matches always use the Short Game Length (ie. 4 waves of zeds then the boss wave). The only difference is you'll notice pale zeds among the enemy waves. These are zeds controlled by enemy players and they may have extra abilities not seen in normal gameplay (such as the Siren's ability to hold a player in place with a focused scream).
When playing as the zeds, you will find yourself with a set of abilities depending on what zed is assigned to you. Should you die, you will respawn as a different zed as long as there are still zeds left to be spawned for that wave. You will never spawn as a Cyst, nor will you spawn as any of the enemies added to the game after the Revenge of the Zeds update (Rioter, Gorefiend, Quarter Pound, or E.D.A.R.s).
For the boss wave, a player on the zed team will be selected to play as the Patriarch (no other bosses are available in this mode). Other players on the zed team can spawn as other zeds periodically during the fight, but eventually the spawns run out and the Patriarch player will be by themself.
When there is only one zed left, they will eventually automatically die if they go long enough without engaging a player. This is to discourage zeds from trying to run away and hide to prevent the wave ending.
You can play on any normal Survival map, but cannot play on Holdout-Style maps (like Nightmare) or Objective-Style maps (like Airship). You also cannot play on DieSector, as that map is exclusive to Endless Mode.
Survival VS cannot be played Solo.