AdDuplex has released its latest report going over the usage distribution for the various different versions of Windows 10, now with data for the month of September. As usual, the data is based on the over 5,000 Microsoft Store apps that use the AdDuplex SDK v.2 or higher, and it was collected on September 28.
This month, the Windows 10 May 2020 Update, or version 2004, grew very significantly, increasing its usage share by almost 10% from 24.1% to 33.7%. This makes it the second most-used Windows 10 version, having surpassed the Windows 10 May 2019 Update (version 1903), which saw a corresponding massive drop from 33.5% to 25.7% in usage share. In fact, every version of Windows aside from the May 2020 Update saw a drop. The November 2019 Update (version 1909), which became the most used version just last month, dropped from 35.5% to 34.5%, just barely holding on to its lead. It's highly likely the May 2020 Update will have surpassed it by next month.
Older versions saw smaller drops, with the October 2018 Update (version 1809) falling from 2.4% to 1.9%, and the April 2018 Update (version 1803) seeing a decrease from 2.1% to 1.9%. The Fall Creators Update (version 1709) held on to its 0.7% usage share, while older versions now account for 1% of users, instead of 1.1%. The number of users running Insider builds grew from 0.5% to 0.7%, possibly propelled by the release of the October 2020 Update to the Release Preview channel earlier in the month.
Adoption for the Windows 10 May 2020 Update began ramping up last month, and you can see that the May 2019 usage has been shrinking quickly. That update is nearing the end of support, as it will end on December 8, so those users are likely being upgraded automatically by now.