Players who purchase the Vault Edition will receive 10 hours of Double XP Tokens and 10 hours of Double Weapon XP Tokens for use in Call of Duty: Modern Warfare II. XP Tokens will be waiting for you and available to use in-game at launch.

However, if you do own Modern Warfare 2, then Warzone 2 has appeared within the main menu as an option, so you don't need to install it separately.