Squid is a fully-featured HTTP/1.0 proxy with partial HTTP/1.1 support
The 3.1 series brings many new features and upgrades to the basic
networking  protocols. A short list of the major new features is:

 * Connection Pinning (for NTLM Auth Passthrough)
 * Native IPv6
 * Quality of Service (QoS) Flow support
 * Native Memory Cache
 * SSL Bump (for HTTPS Filtering and Adaptation)
 * TProxy v4.1+ support
 * eCAP Adaptation Module support
 * Error Page Localization
 * Follow X-Forwarded-For support
 * X-Forwarded-For options extended (truncate, delete, transparent)
 * Peer-Name ACL
 * Reply headers to external ACL.
 * ICAP and eCAP Logging
 * ICAP Service Sets and Chains
 * ICY (SHOUTcast) streaming protocol support
 * HTTP/1.1 support on connections to web servers and peers.
   (with plans to make this full support within the 3.1 series)