As opposed to previous years, the spring Windows 10 update is coming in late May, with Microsoft giving it a full month of testing in the Release Preview ring. The company has been slowly updating all of its documentation to reflect version 1903, and for the first time, it has increased the minimum storage requirement for the OS.
Previously, the requirement was 16GB for 32-bit and 20GB for 64-bit. Now, you'll need 32GB for either version.
Spotted by Pureinfotech, it comes from the Minimum Hardware Requirements page, which really hasn't been updated much since Windows 10 version 1703, a version that was released two years ago. For example, the entirety of section two is devoted to Windows 10 Mobile, and the PC processor requirements in section 3.1 still say that you need an x86 or x64 CPU. It even lists Windows Server 2016 as the latest version, with no mention of Server 2019.
Today's change won't affect many people, if anyone. There are few enough devices with 32GB of storage, let alone PCs with less than that. If you do have a Windows 10 PC with 20GB or less of storage, and they do exist, you've probably been thinking about buying something new anyway, so now is the time.