Both DLCs are set after the events of the main game, and introduce two new episodes to conclude the story. The first DLC was originally made free to players who bought a new copy of the original game, with the second costing $6.99.
The discount follows the release of developer Remedy's latest game, Quantum Break, earlier this week, which also included free download codes for Alan Wake and its DLCs to all pre-order customers.
The full game, meanwhile, remains available to purchase from Xbox Live for £14.99.
Remedy has previously said that it would "love [the] opportunity to do more" Alan Wake, and that discussions about a sequel remain ongoing.