Moved to Forum: Original Link
Reason: Deal poster mislabelled the game as Free to Play, which implies that the full AOE III experience could be played without paying. It has been later clarified that this is a game demo with some cut content (but includes unlimited playtime and unrestricted access to Multiplayer with all 16 Civilisations selectable).
Age of Empires III: Definitive Edition is launching a new way to play! For the first time, new players can now join the ranks of this historical and stunning RTS experience with a rotating roster of the game’s 16 civilizations which can be played in both single player and multiplayer games FREE of purchase on Steam.
Now is the time to try Age of Empires III: Definitive Edition! Play for the first time or current AoE III: DE players can invite their friends for epic battles in striking 4K Ultra HD graphics.
Starting today, AoE III: DE will be offering new players the opportunity to play from a selection of rotating civilizations and other features like the ‘Blood’ Story Mode campaign, the Algiers Historical Battle, along with the tutorial and The Art of War challenge. And now, all players will be able to join in on monthly global events to unlock new Hero Cosmetics!
Information added 11-May-2024 for more context as to what this game includes:
The trial version provides access to a rotating roster of the full game's 16 civilizations to play freely in both single player and multiplayer games, a first look at the 'Blood' Story Mode campaign, the Algiers Historical Battle, along with the tutorial and The Art of War challenge missions to learn and master the game.
Jump online to play with your friends or to battle your way through a select group of random maps in skirmish games against the AI. Whichever way you choose to play, you will enjoy the stunning graphics, the fully remastered soundtrack, and modernized RTS gameplay in this third installment of the award-winning Age of Empires franchise.
AOE3 Free to Play, that was unexpected.
I got AOE4 and ended up going back to AOE2:DE, it originally came out in the 1900's and it still hasn't been topped.