Whilst I was off work last week TFS 2018 Update 3 was released. As stated in the 2018.3 release notes this is the final bug fix update release of TFS 2018.

The next major release of TFS will not be named TFS 2019 as you might have expected, but will use the new name of Azure DevOps Server. You can see the features planned for this next release in the Azure DevOps Features Timeline