As of Mantis 1.1.0a4, MantisConnect web service will be released out-of-the-box with Mantis under the GPL license. The MantisConnect project will remain focused on the client libraries for the web service and useful tools on top of such libraries. MantisConnect currently has client libraries in C#, Java and Cocoa. It also includes tools like Eclipse Plug-in, Mylyn-Mantis Mylar Connector, NAnt task, Mantis Notifier, Cropper Plugin, and others.
In the future, other APIs may be released like XML-RPC, REST, etc. Work on such APIs will depend on demand and contributions. For now, SOAP will remain the main API for remote access to Mantis.