Comparison HTTP/1.1 and HTTP/2

HTTP 1.1 was released 1997 and  

• Was originally composed for HTTP GET and POST.
• Works with Request/Response and not server push
• Do not compress HTTP headers. Today are many HTTP headers used.
• Opens a new TCP connection to a server at each request

 
HTTP/2 was released in 2015
 

• Supports multiplexing. Client and server can push messages in parallel over the same TCP connection, which reduces latency.
• Supports server push streams (multiple messages) for one request from the client.
• Supports header compression.

Reference: https://developers.google.com/web/fundamentals/performance/http2