There are two updates available now for Configuration Manager current branch version 1806. You will see only the update applicable to your site.
Administrators who opted-in to the first (early) wave deployment for System Center Configuration Manager current branch, version 1806, and downloaded it before August 10, 2018, have an update available in the Updates and Servicing node of the Configuration Manager console. This update, made available on August 31, 2018, addresses important late-breaking issues that were discovered during the final release process for version 1806.
For more information, including the issues fixed and the applicability of the update, please read:
4346645 : Update for System Center Configuration Manager version 1806, first wave – https://support.microsoft.com/help/4346645
Administrators who downloaded System Center Configuration Manager current branch, version 1806 between August 10, 2018 and August 24, 2018 have an update available in the Updates and Servicing node of the Configuration Manager console. This update, made available on August 31, 2018, addresses important upgrade-related issues for version 1806.
For more information, including the issues fixed and the applicability of the update, please read:
4459354 : Interoperability update for System Center Configuration Manager version 1806 – https://support.microsoft.com/help/4459354
Additionally, if you are looking for the summary of fixes in Configuration Manager current branch 1806 you’ll find it here:
4459701: Summary of changes in System Center Configuration Manager current branch, version 1806 - https://support.microsoft.com/help/4459701