Microsoft is releasing a new Windows 10 Cumulative update. to the Release Preview Ring for Windows 10 1809.
Cumulative Update KB4490481 requires the OS to build 17763.404, and like most Cumulative Updates to the Release Preview Ring, a changelog is not available.
However, it is probably testing fixes for next week’s Patch Tuesday. In the Release Review Ring, Windows 10 Insiders can download the update by checking for Settings Updates.