https://www.techradar.com/news/world-of-warcraft-classic-turns-back-time-but-keeps-contemporary-bells-and-whistles

Blizzard has revealed more details on exactly how World of Warcraft Classic will pan out, with the nostalgic spin on the MMO set to be based on the game as it was during Patch 1.12 (known as Drums of War).

Drums of War went live in August 2006 and was the last patch before the first big expansion for the game landed (Burning Crusade arrived at the start of 2007). Blizzard said it took much deliberation over exactly where to pitch WoW Classic, and chose this point because it “represents the most complete version of the classic experience”.