Halo 4's "Crimson" map pack was released today, and it seems some users have been able to access it for free.
Of course, the 2,000 Microsoft Point "War Games Map Pass" gives players access to "Crimson" and two more upcoming map packs anyway, but according to commenters on Joystiq's article, even those without the Map Pass can download today's pack for free.
If so, it's likely an error that Microsoft will soon correct. Otherwise, the "Crimson" map pack costs 800 Microsoft Points (around $10). It includes the Wreckage, Harvest, and Shatter maps, with a new playlist that features the three new levels exclusively.