An old Left 4 Dead prototype was inadvertently put into a recent Counter-Strike 1.6 update

Earlier this month, Valve updated its original Half-Life game with some new content, along with some graphical upgrades, to celebrate its 25th anniversary. However, the developer also quietly updated its Counter-Strike 1.6 multiplayer shooter earlier this week with some of the engine and graphics updates as well so it would work with the Half-Life update.

As it turned out, that update from Valve also included the earliest prototype for one of the developer's other major games, Left 4 Dead. The leaked prototype was posted on X (formerly Twitter) by @GabeFollower (via PC Gamer).

The prototype was called "Terror Strike" and it used assets from Counter-Strike to demonstrate the zombie swarm gameplay that would eventually be used a few years later in Left 4 Dead. Counter-Strike community members found that early code in the update and got the prototype to work.

In this early version terrorists have to plant a bomb in the map while also fighting off counter-terrorists, except they would come back as zombies after being killed by the terrorists. Once the bomb is planted, any counter-terrorists that were turned into zombies respawn once again and attempt to kill the terrorist players.

It's always interesting to see these kinds of early prototypes for games, which show some of their basic ideas and designs before they are fully fleshed out (no pun intended).

Right now there's no indication that Valve has any plans to launch a new Left 4 Dead game. The company's latest title, aside from the Half-Life anniversary update, was the launch of the free-to-play Counter-Strike 2 a few months ago, which replaced the older Counter-Strike: Global Offensive.