Hello,
It seems like that there is no API documents for WSUS on Windows Server 2012 and above.
There are tools that can user WSUS API to demonstrate centralized monitoring and reporting for WSUS in Windows Server 2012 and above, please refer to the link below for more details:
https://docs.microsoft.com/en-us/windows-server/administration/windows-server-update-services/manage/wsus-tools
Regards,
Yan Li
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