https://wccftech.com/wow-classic-patch-1-12/

Blizzard’s upcoming vanilla server option for World of Warcraft, WoW Classic, will use patch 1.12 as the foundation for the game.

That’s what the developers confirmed in a recent developer post on the official World of Warcraft blog. World of Warcraft Classic was officially announced last year, but details about the vanilla server option have been scarce.