Source SDK Base 2013 Multiplayer

From Exterminatus Manual

++Getting Started++

What is it?

Source is the name of the game engine that Half-Life 2 used. SDK stands for Software Development Kit. Base because it's the basis of a first person shooter (without actually being playable). 2013 relates to the year this version of Source initally started development. The SDK Base comes in Single and Multiplayer variations, with different content, we want the multiplayer version as EX is a multiplayer game. This "tool" grants mod makers access to the content and binaries that are standard to multiplayer Source games.

We'll call the the "SDK Base" from here on.

How do I get it?

The SDK Base is free and can be Installed from the Tools area of the Steam Library.

Updates

When you first install the SDK Base and whenever Valve updates it via steam, you need to launch the SDK Base from the tools tab before you will be able to play Exterminatus. If you try and launch Exterminatus and nothing seems to happen it probably means you need to run the SDK base again.