Stephen Spector said on Xen.org that the first meeting of the Xen API Community Project has taken place. If you missed it or are interested to learn more, the meeting minutes are available on the Xen Wiki.
This project is collaborating around a central document, titled "Xen Management API", presenting our ideas in terms of a data model, with an implied binding to XML-RPC calls. These XML-RPC calls can then be used (over one of a number of transports) to manage a Xen-based system.
The intention is to standardise both the data model and XML-RPC calls (one implying the other) and then the Xen project will guarantee that that wire protocol would be supported for the long term.
Behind that interface, we would then be free to improve Xend, and at the same time we give a solid foundation for third-party tools (in particular libvirt-based applications), GUIs, and so on. The API becomes effectively part of the "guarantees" of the Xen project.
Stephen added that a follow-up meeting will be scheduled for later this month or early June to discuss the existing Xen API specifications with an emphasis on comparing them to the Citrix XenServer API definitions available at http://community.citrix.com/display/cdn/XenServer%20SDK. If you are interested in assisting in this project, there is still time to make your voice heard. Read the API specifications and attend the next meeting.