It's been a long journey with so many brain stormings and thought experiments, and it's amazing that we finally managed to release the first alpha of the new major Netty version, 4.0.0.Alpha1.
As usual, you can get it here or in the Maven central repository.
Before rushing into your IDE and updating your class path, you might want to spend some time to read about what's new and how to migrate your applications from 3.x to 4.0, since 4.0 introduces numerous backward incompatible changes. Those changes are of course for good reasons and I hope you like them. Please feel free to ask questions about the problems you encounter during migration - I'm eager to help you!
However, please also note that the new API is not final. It's still at the alpha stage and it might change as we find design flaws or better ways to do the same thing. At the same time, there are so many opportunities where your constructive feed back will make 4.0 better than ever. Let me look forward to your joining the developer group and letting people know what you think.