ViVe is a C# library you can use to make your own programs that interact with the A/B feature experiment mechanism found in Windows 10 & newer.
In case you'd like to talk to NTDLL exports directly, you can use its NativeMethods.
Otherwise, RtlFeatureManager offers the same featureset with the benefit of some struct heavy lifting being done for you.
ViVeTool is both an example of how to use ViVe, as well as a straightforward tool for power users which want to use the new APIs instantly.
In order to use ViVe, you must be running Windows 10 build 18963 or newer.