Little is known at this point about the DLC apart from it will be called Slingshot and will feature an extra character from the original XCOM game plus some extra missions. We will update as more information comes out.
PC System Analysis For XCOM: Enemy Unknown Slingshot Requirements
4 GB will also be needed to achieve the XCOM: Enemy Unknown Slingshot rec specs and get 60FPS. XCOM: Enemy Unknown Slingshot needs a graphics card thats at least as powerful as a GeForce 8600 GT 512MB GDDR3/Radeon HD 2600 Pro paired with Athlon 64 X2 Dual Core 4400+/Core 2 Duo E4400 2.0GHz CPU to match the min specs. This PC setup will deliver 25-35 Frame Per Second at Low graphics setting on 720p resolution. Your PC needs 2 GB system memory as well for min.