Halo 5: Guardians is free to play on Xbox One this weekend as part of Microsoft’s Free Play Days program.
From now until Sunday, January 13th, Xbox Live Gold members can download and play the game for free. All progress made during this free weekend can be carried over to the full game, if players choose to purchase it.
— Halo (@Halo) January 10, 2019
In addition to the free weekend, the game and its Digital Deluxe Edition, which contains the Warzone REQ Bundle and Halo: The Fall of Reach, are discounted.
Halo 5: Guardians originally released for Xbox One in 2015.