Major Nelson has confirmed on Twitter that the followup to Alan Wake will be a downloadable title, and not a retail release.
The "We can confirm that this new “Alan Wake” game will be a fully standalone experience and released on Xbox LIVE."reads,
Not much has been known about Alan Wake: Night Springs, save a image last June. Last month, Remedy's Oskari Hakkinen said about the game; "this next Wake installment will not be Alan Wake 2. And neither will it be DLC."