In release notes in 'Technical preview' section, bullet 'Server-Sent Events in Java (SSE)' states:

An implementation of the Server-Sent Event Model in Java is provided for customers working with mobile and rich clients. This includes the server and client implementation. This is a technical preview only.

Although there is no client implementation IMHO. Also per this comment. I would rather simply use exactly same text that was used in EAP7.0.0 Release notes:

An implementation of the Server-Sent Event Model in Java is provided for customers working with mobile and rich clients. This includes only the server implementation. This is a technical preview only.