"Many people do not realize that CSPromod really isn’t a mod at all. It’s a total conversion, and only shares assets such as models and textures. Because we’ve never had any access to the CS 1.6 or CS:S source code, there’s never been anything to actually, well, modify. We had no access to any of the CS 1.6 or CS:S weapon code, movement code, logic code – nothing; not even the basic structure of Counter-Strike itself (scoring system, team system, bomb plant/defuse system, etc.). We had to recreate the entire game from scratch code-wise. If you open up the HL2SDK, you’ll see exactly what we started with. In fact, the only parts of CSPromod that aren’t entirely, 100% custom-made are the assets (models, textures, and skins). As you all know, those will also be replaced with custom assets in the near future.

The fact that, code-wise, CSPromod isn’t actually a mod, but rather a completely custom-built game, accounts largely for the massive amount of time it’s taken so far. The current iteration of the project was restarted from scratch in the beginning of 2007 (unfortunately, all of our progress and effort in 2006 was wasted, as we went through three head programmers that year who all turned out to be unreliable and disappeared with our code base). So what you’re looking at is 3 years of work done by a very small development team of three coders, a mapper, and a project manager, all working on a volunteer basis in their spare time."

Taken from the promod website.

"We had to recreate the entire game from scratch code-wise"