Download and install now option provides users a separate control to initiate the installation of a feature update on eligible devices with no known key blocking compatibility issues. Users can still “Check for updates” to get monthly quality and security updates. Windows will automatically initiate a new feature update if the version of Windows 10 is nearing end of support. We may notify you when a feature update is available and ready for your machine. All Windows 10 devices with a supported version will continue to automatically receive the monthly updates. This new “download and install” option will also be available for our most popular versions of Windows 10, versions 1803 and 1809, by late May.
5 月末予定の Windows 10 May Update（バージョン1903）から。
I’m pleased to announce that the Windows 10 May 2019 Update will start to be available next week in the Release Preview Ring for those in the Windows Insider Program. We will begin broader availability in late May for commercial customers, users who choose the new May 2019 Update for their Windows 10 PC via “check for updates,” and customers whose devices are nearing the end of support on a given release.
“check for updates,” で更新されるのは broader availability in late May だけどなぁ
1803 / 1809 にインストールオプションが表示されるのも late May だからつじつまが合わない