For those interested, they at least have a medium size write-up how they created this technically: https://worldofwarcraft.com/en-us/news/22646759/restoring-hi

For those interested, they at least have a medium size write-up how they created this technically: https://worldofwarcraft.com/en-us/news/22646759/restoring-history-creating-wow-classic-panel-recap https://worldofwarcraft.com/en-us/news/22646759/restoring-hi... Here is a live blog of the Blizzcon talk: https://www.wowhead.com/news=288407/blizzcon-2018-restoring-history-creating-wow-classic-panel https://www.wowhead.com/news=288407/blizzcon-2018-restoring-... My take is one of the original programmers for WoW still at work's at Blizzard and helped great deal with this effort. They were also able to go back in their source Control and pull the code from back then and they've been different current code to previous code in various places to see how behaviour has changed. And then Ford porting old behavior onto a existing client.