Microsoft will not support a semi-annual release channel in the forthcoming Windows Server 2022, and users requiring frequent updates will be directed towards Azure Stack HCI (Hyperconverged Infrastructure).
In the old Windows Server world, users could choose between the Long Term Servicing Channel (LTSC) and Semi-Annual Channel (SAC) for installations, with LTSC being essentially the traditional model of a big release every two or three years, and SAC being more the “as-a-service” model with frequent feature updates to get the latest technology.
Businesses installing Windows Server for general-purpose use would normally use LTSC, which has five years of mainstream support and five years of extended support. The purpose of SAC is for container workloads (host or container image) or scenarios where a VM is short-lived and easily replaced. Limitations of SAC include only 18 months of support per release, a requirement for Software Assurance (a more expensive subscription license), and no desktop experience option.