Although v1809 has been available for sometime. You had to force the install. The normal Windows Update did not find it.
In some cases, you could manually ‘Check for updates’ and it would show up. But not always. And I don’t know why.
The next method was to download v1809 and put it on a thumb drive. Run the ‘setup’ program after you log into your Windows 10 PC. A few more steps but that worked every time that we did it.
This release from Microsoft implies that you will be getting v1809 in the next few weeks.