@andstatus the URI (as in the context of Atom post id, which !GNUsocial uses as a transport format) cannot be assumed to have a discernible structure. It can be any character combination, or at least only as restricted as in the Atom standard.

The URI is available in the post's raw atom formatted representation. It is probably still not available in the Twitter compatible API because it was never designed for federation. I don't believe I have ever recommended anybody to use the Twitter compatible API because of its limitations.