Windows Experience blog: introducing Windows 10 Version 21H1 #WinTen21H1
Those reading the subject line carefully may have noticed a new hashtag: #WinTen21H1. And yes, 21H1 is now official:
Note: although the title says “Windows 10, version 21H1”, this forum will continue to use the term “Version 21H1”. As stated in the blog post and confirmed elsewhere, it will be build 19043 (another enablement package).