https://wccftech.com/microsoft-automatic-rollout-of-windows-10-1809/

Around Christmas, Microsoft began delivering an update that would start automatically pushing the latest Windows 10 October 2018 Update to computers. However, the company didn’t acknowledge this and we continued to suggest readers to hold on to installing this particular version of Windows 10.

The company has now officially announced that it has started the phased rollout of Windows 10 October 2018 Update via Windows Update and that version 1809 will be made available to devices that are believed to be the most compatible with the update.