https://www.techradar.com/news/windows-10-april-2018-update-is-finally-coming-to-all-alienware-laptops

Shortly after Microsoft released its major Windows 10 April 2018 Update, it emerged that some Alienware notebooks were being blocked from installing the upgrade. However, it now looks like the block has been lifted.

The Alienware Support Twitter account confirmed to Mayank Parmar of Windows Latest that “Microsoft update 1803 is now ready for Alienware computer. This one should run automatically already, if no feel free to run it. It works now.”