Left 4 Dead – Valve “accidentally” releases early prototype of the first game

Half Life recently celebrated its 25th birthday and to mark the occasion, both the game and Counter-Strike 1.6 received an update, among other things to make some technical features such as higher resolutions and Steam Deck support available.

With this update, however, a very early prototype of the first part of Left 4 Dead was also released – apparently by mistake.

Very first prototype in CS:CZ

The prototype is called “Terror Strike” and is based on Counter-Strike: Condition Zero, which was also co-developed by Left 4 Dead developer Turtle Rock Studio.
However, it is more of a very simplified representation of the core gameplay of Left 4 Dead, which was implemented with Counter-Strike assets and the simplest effects.

In the prototype, the player starts at a spawn and buys weapons to then use the bomb to get to one of the spots. Zombie CTs, armed only with a knife, stand in his way and charge towards him.
As soon as the bomb is planted, all the CTs spawn again and try to eliminate the player and/or defuse the bomb.
Some custom sound effects can also be heard in the video.

The prototype was discovered by a user who calls himself “Gabe Follower” on Twitter and published a video there.
According to him, another user called “The One Epicplayer” ported the map and also got the bots working again, which then led to this result:

The prototype is apparently also playable on other maps, as another video shows it in action on the Inferno map:

Whether the whole thing was really an oversight on Valve’s part or whether they knowingly published this piece of gaming development history is anyone’s guess.
In the meantime, the code has probably disappeared from the game files, but anyone who wants to can still download the prototype and test it for themselves.