The base game is required (included with Game Pass).
These 3 paid DLC are now free for owners of the game. Note that while it is also included for new buyers the regular price of the game has increased from $22.95 to $39.95 (currently on sale for $13.98 at the Xbox AU store).
To celebrate, starting today new players can purchase Age of Empires II: Definitive Edition and will automatically receive three DLCs: Lords of the West, Dawn of the Dukes, and Dynasties of India. By combining these DLCs with the base game, we’re offering a more complete experience to newcomers for only $34.99 (USD, please check stores for your local price).
For players who already own Age of Empires II: DE on Steam, Microsoft Store or Xbox, we want to thank you for playing with us these past five years by automatically gifting you any of the three mentioned DLCs that aren’t already in your collection. You can find instructions on downloading additional content on our Support Site.
Does Game Pass count as owning?