> For example, measurements of Flywheel’s workload show that 42% of HTML bytes on the web that would benefit from compression are uncompressed, > despite GZip being universally supported in modern web browsers [13]. This is in part because GZip is not enabled by default on most web servers, > yet only a single-line change to the server configuration is needed.

So really, it's a gzipping proxy written in Go. Hopefully they extend the protocol to better compression in future.