Microsoft never sleeps. In addition to its steady releases of major and minor updates to the current version of Windows 10, the company frequently rolls out public preview builds to members of its Windows Insider Program, allowing them to test out — and even help shape — upcoming features.
Microsoft numbers Windows 10 releases using a YYH1/YYH2 format, with the YY standing for the last two numbers of the year and H1 or H2 referring to the first or second half of the year. So the most recent version of Windows 10 is officially referred to as Windows 10 version 21H1, or the May 2021 Update. The next feature update, due in the fall of 2021, will be version 21H2.