I am actually unsure of the licensing situation. I believe the SDK is supposedly built from the source releases. And AFAIUI Apple’s license is BSD-like. However, parts of the SDK, like XPC don’t have released sources, though we do need XPC in particular if we go with the source releases too. So I think linking to the SDK is fine. Although some source releases, like network_cmds, aren’t part of it. And some headers might only be in the source releases, I think that may be the cause for the scproxy problems.