The Siberian Ranger Pack DLC is available now to those of you who already have the Season Pass. If you don't have the Season Pass, you can purchase the pack for $2.99. The pack includes the "Siberian Ranger" outfit, increasing Lara's capacity for carrying special ammunition, the "Accipiter Nox" pistol skin, and a card pack containing a rare card and increased chances for more rare cards. Enjoy!
Source: Official Tomb Raider Blog