You need base game for Steam only to get this DLC but for other platforms you can have it without base game even via Epic games regardless of condition to have base game.

SYSTEM REQUIREMENTS

MINIMUM:

• OS: Windows 7 SP1, Windows 8.1, Windows 10 (64-bit versions only)
• Processor: Intel Core i5-2400S @ 2.5 GHz or AMD FX-4320 @ 4 GHz or equivalent
• Memory: 6 GB RAM
• Graphics: NVIDIA GeForce GTX660 / AMD R9 270X (2GB VRAM with Shader Model 5.0 or better)
• Storage: 50 GB available space
• Sound Card: DirectX-compatible using the latest drivers

RECOMMENDED:

• OS: Windows 7 SP1, Windows 8.1, Windows 10 (64-bit versions only)
• Processor: Intel Core i7- 3770@ 3.5 GHz or AMD FX-8350 @ 4 GHz or better
• Memory: 8 GB RAM
• Graphics: NVIDIA GeForce GTX970/GTX 1060 or AMD R9 390/RX480 (4GB VRAM with Shader Model 5.0 or better)
• Sound Card: DirectX-compatible using the latest drivers