CDT 9.0.0 is a major release that ships with the Neon simultaneous release. It fixes bugs and brings new features which are listed in the corresponding CDT New&Noteworthy page. This is the first major release of the CDT project since June 2011. Consequently, and after warning extenders over a year in advance, major cleanup was done to remove deprecated APIs and components. Details of API-breaking changes can be found here. Of particular importance is the removal of the CDI framework for debugger integration; it has been replace many years ago with the DSF framework also provided by the CDT.
Two additional components that while used by the CDT aren't functionally part of CDT is the Launch Bar and the Templates Engine. The Launch Bar has a number of API changes for this, it's 2.0 release, to support more flexible launch targets. The Templates Engine is new and supports new file and project content using the Freemarker template engine.