There is a more complete FAQ available under Eclipse4/FAQ
This FAQ describes what the new 4.x stream is about, what to expect from it, and who should be interested in it. For questions about development using the Eclipse 4 Application Platform, see the E4AP RCP documentation and its FAQ.
When was the Eclipse 4 SDK released?
The first release of Eclipse 4 was in July 2010. The current Eclipse 4.2 release was released in June 2012. The Juno Release Train in 2012 was the first time Eclipse 4 was the base platform for the release train. Previously, the platform was Eclipse 3.x.
Where can I download it?
The Eclipse 4 is part of all the packages found on the eclipse.org/download. It can also be downloaded from from this location.
What are some of the known issues with the Eclipse 4 SDK?
Please see Eclipse release notes for list of known issues.
How does Eclipse 4.x differ from 3.x architecturally?
The Eclipse SDK 4.x, for the most part, contains all the plug-ins that make up Eclipse 3.8. That is, all of JDT and PDE, and most of the Platform, are the same bits as in 3.8. What's different is the implementation of the Workbench, i.e. the org.eclipse.ui.workbench plugin, and the technologies this new implementation is based on. Before the release, the technologies (modeled UI, dependency injection and service-based programming model, CSS-based styling) were called 'e4' but we are now referring to them as the Eclipse 4 Application Platform or E4AP. On top of the Eclipse 4 Application Platform, the 4.x Workbench offers an implementation of the 3.x Workbench APIs, to provide backwards compatibility mainly for the Eclipse IDE.
Why Eclipse SDK 4.x?
In 2007, the Eclipse Project leadership decided some major changes were needed in the Eclipse platform. See this EclipseCon 2008 talk for more details on the motivation and thinking behind these changes. It would have been too disruptive to attempt these changes within a single annual release cycle, so a new incubator project was started to run in parallel to normal Eclipse project development. Several pieces of technology from this incubator have since matured and are ready for wider consumption. Some of these changes have already been integrated in the annual Galileo and Helios releases.
For the biggest changes, we want to provide the community all the time it needs to adopt this new technology, so the 4.x stream was created to allow for 3.x and 4.x releases to occur in parallel. In 2010 and 2011 there were parallel 3.x and 4.x stream releases to allow clients to stage their adoption of the new platform technology at their own pace.
What is e4?
E4 is a sub-project of the Eclipse top-level project. It is an incubator where we can play around with different ideas about the future direction of the platform. It is a place where we can quickly bring in new committers so they can try out their ideas. It is our playground. Some of these ideas will bear fruit and migrate into other mature projects, and others will remain in the incubator.