Ubisoft has announced the PC specs for Rainbow Six Siege:

MINIMUM

Supported OS

Windows 7, Windows 8.1, Windows 10 (64bit versions required)

Processor
Intel Core i3 560 @ 3.3 GHz or AMD Phenom II X4 945 @ 3.0 GHz

RAM
6GB

Video Card
NVIDIA GeForce GTX 460 or AMD Radeon HD 5870 (DirectX-11 compliant with 1GB of VRAM) [See list of supported video cards down below]

DVD ROM Drive
DVD-ROM Dual Layer

Sound
DirectX® 9.0c compatible sound card with latest drivers

Hard Drive
30GB

Multiplayer
Broadband connection with 256kbps upstream or faster

RECOMMENDED

Supported OS

Windows 7 SP1, Windows 8.1, Windows 10 (64bit versions required)

Processor
Intel Core i5-2500K @ 3.3 GHz or better or AMD FX-8120 @ 3.1 Ghz or better

RAM
8GB

Video Card
NVIDIA GeForce GTX 670 (or GTX 760 / GTX 960) or AMD Radeon HD 7970 (or R9 280x [2GB VRAM] / R9 380 / Fury X) [See list of supported video cards down below]

DVD ROM Drive
DVD-ROM Dual Layer

Sound
DirectX® 9.0c compatible sound card 5.1 with latest drivers

Hard Drive
47GB

Multiplayer
Broadband connection with 512kbps upstream or faster

SUPPORTED VIDEO CARDS AT TIME OF RELEASE

NVIDIA

GeForce GTX 460 or better, GTX 560 or better, GTX 650 or better, GTX 750 or better, or any card from the GT900 and Titan Series

AMD
Radeon HD5870 or better, HD6870 or better, HD7770 or better, R7 260X or better, or any card from the R-300 series and Fury X

Laptop models of these cards may work but are not supported. These chipsets are the only ones that will run this game. Additional chipsets may be supported after release. For an up-to-date list of supported chipsets, please visit the FAQ for this game on our support website: http://support.ubi.com