Feature updates for Windows Server 2016 will also be released twice a year in the near future. This means that the update behavior is similar to Windows 10. However, Windows Server 2016 will offer the option of selecting the "Long-term Servicing Channel", which means that new features will only be released every two to three years.
So far I could not find any information whether the channel can be selected after the installation or whether there will be a separate version for the Long-term Servicing Channel (similar to Windows 10 LTSB).
At the same time, it will also be possible to test the new Windows Server versions as an Insider Preview. This procedure was also introduced with Windows 10. As with Windows 10, the new server versions can be tested quite early.
There will therefore be two options for Windows Server 2016 in the future, Long-term Servicing and Semi-annual Channel:
Source: Windows Server Semi-annual Channel Overview
Long-term Servicing Channel
The Long-term Servicing Channel roughly corresponds to the current release model. A new Windows Server version is released every two to three years. What is new is that these updates can now be distributed via Windows Update, WSUS or System Center Configuration Manager. Before Server 2016, it was only possible to upgrade the existing installation. For the Long-term Servicing Channel, there is 5 years of mainstream support and a further 5 years of extended support.
Semi-annual Channel
With the semi-annual channel, there will be new functions for Windows Server twice a year. Microsoft plans to release the feature updates in spring and fall. Each feature update will include 18 months of support. The Semi-annual Channel will only be available in the volume licensing program with Software Assurance, in the Azure Marketplace, Cloud/Hosters and in the MSDN program.
Windows Insider for companies
If you want to test new versions of Windows Server in advance, you have to register in the Windows Insider Program for companies:
The new server versions can then be tested in advance via the Windows Insider Program for companies. The first preview is due to be released soon.