TerraDave
5ever, or until 2024
In the wired article Chris said that D&D had its best ever sales in November and that xgte was the best initial sales of any d&d book ever.
Could certainly see the best ever part, but I still don't know what "fastest" meant. We know it did not hit #1 overall like the PHB did, but could be some other metric. Amazing for a supplement (in a game with 3 core books) in any case.