I am sorry, I found the answer to my own question: HTTP/2 uses SPDY as a jumping-off point. HTTP/2, however, uses a fixed Huffman code-based header compression algorithm, instead of SPDY's dynamic stream-based compression. This helps to reduce the potential for attacks on the protocol. Posted at Nginx Forum: http://forum.nginx.org/read.php?2,261727,261761#msg-261761