Alan Wake, which released May 18, arrives on the Xbox Live Marketplace's Games on Demand service six months later.
Major Nelson listed Alan Wake in his most recent update; it'll get here Nov. 23. A price wasn't listed in North America but MCV reports it'll be £19.99 in the U.K.; those who balked at it full price might be seeing it for a third of that.
MCV notes, as we all know, that major Games On Demand listings typically don't happen until a year after the game's retail release. This being an Xbox 360 exclusive published by Microsoft Game Studios may have much to do with the shortened time.