Here’s a leak of sorts, as the official WotLK Classic site had the expansion’s release date up for a short while and then took it down. 

The date was September 26th 2022, but it seems it wasn’t ready for public release yet. Whether that indicates the date isn’t quite set in stone yet or just that the announcement wasn’t planned for today/was postponed we can’t be sure, but here’s the old and new sites (via redditor EversorA and StaysafeTV):