2015-09-17 The HTTP/2 implementation was commited to trunk.
See: http://hg.nginx.org/nginx/rev/257b51c37c5a

2015-09-11 Version 6 (NGINX 1.9.4)
 - Sending GOAWAY frame on connection shutdown;
 - Proper handling of huge response headers using CONTINUATION frames;
 - Various minor fixes.

2015-09-08 Version 5 (NGINX 1.9.4)
 - Validation of the request headers;
 - Improved error handling even more;
 - Added the http2_max_header_size directive that limits the maximum size of
   a request headers (16384 bytes by default);
 - Fixed the default value of the http2_max_field_size directive;
 - Limited consumption of memory during the HTTP/2 session;
 - The $request_line variable for HTTP/2 requests now uses "HTTP/2.0" as
   the version token instead of "HTTP/1.1".

2015-08-31 Version 4 (NGINX 1.9.4)
 - Improved error handling;
 - Added the http2_max_field_size directive that limits the maximum size of
   a request header field (4096 bytes by default);
 - The http2_keepalive_timeout directive was renamed to http2_idle_timeout.

2015-08-19 Version 3 (NGINX 1.9.4)
 - The gzip and gzip_static modules might not work with HTTP/2 requests;
 - Fixed processing of Cookie headers.

2015-08-14 Version 2 (NGINX 1.9.3)
 - Introduced NPN support for HTTP/2 negotiation (this reduces OpenSSL version
   requirement to 1.0.1+);
 - Various fixes in the prioritization mechanism;
 - Fixed missing "Location" response header in some configurations;
 - Fixed processing of the ":authority" pseudo-header (the HTTP/2 analog of
   the "Host" header).

2015-08-05 Version 1 (NGINX 1.9.3)
The first public alpha release.