HttpClient 3.1 adds support for the RFC 2965 cookie management (also known as Cookie2 or port sensitive cookies) and a number of improvements to the HTTP connection management. HttpClient 3.1 is backward compatible with HttpClient 3.0
HttpClient 3.1 is likely to be the last non-bug fixing release of the HttpClient 3.x code line
Current Stable Release (recommended): Release 3.1
HttpClient 2.0 is no longer being actively developed and supported.