The 3.1 branch of Commons HttpClient is now in the maintenance mode. Bugs will still be fixed, but no new features added.
HttpCore 4.0 is almost fully feature-complete and its API has been frozen. All official releases in the 4.0.x code line are expected to be API compatible. The focus of the development efforts will be gradually shifting towards providing better test coverage, documentation and performance optimizations.
The HttpCore forms the foundation of HttpClient 4.0 and can also be used separately to build custom client- and server-side HTTP services.
The complete list of bugs and new improvements targeted for the next release can be found here.
The major part of the Httpclient redesign is now complete. The first four ALPHA releases fixed most of the known architectural deficiencies and problems. HttpClient now sports a cleaner, more flexible and expressive API, a more modular structure, improved performance and reduced memory footprint.
The new API will be further improved and revised in the course of the ALPHA development phase. HttpClient 4.0 is still considered experimental and should be used with caution.
The only feature that has not yet been ported to the new API is the NTLM authentication scheme.
The complete list of bugs and new improvements targeted for the next release can be found here.