For some unknown reason, rather than hosting the anniversary on the day it occurs, ie the 23rd of Nov, Blizzard are instead giving the achievement between November 30th and December 14th.
The sixth anniversary of the launch of World of Warcraft is coming on the 23rd of November, and if the past two years are anything to go by you will receive a special feat of strength achievement just for logging in on that day. Blizzard have also given out a pet on both those anniversaries, the Baby Blizzard polar bear in 2008 and the Onyxia Whelpling last year but it’s not entirely clear if they’ll be giving one this year.
In a blue post about the upcoming anniversary Blizzard say such pets will be reserved for important milestones in the future.
New bosses added to WoW, elemental invasion steps up a gear
Prepping for realm first 85 achievements in Cataclysm
Arena weapons and armour available for honour pre-WoW: Cataclysm
Tripping the Rifts Feat of Strength
World of Warcraft: Cataclysm Collector’s Edition
World of Warcraft Dungeon Companion, Volume III