Today the Prism Composite Application Guidance for WPF team (Gosh, what a name!) published the first release candidate.

The Composite Application Guidance for WPF is designed to help you more easily build enterprise-level Windows Presentation Foundation (WPF) client applications. This guidance will help you design and build flexible composite WPF client applications – applications that use loosely coupled, independently evolvable pieces that work together within the overall application.

The release description states that the final release will be on MSDN within a couple of weeks.