I've updated
%userprofile%\documents\iisexpress\config\applicationhost.config
per the changes on this post:
http://ben.onfabrik.com/posts/aspnet-web-api-compression
Namely, I've added
<httpCompression ...>
<dynamicTypes>
<add mimeType="application/json" enabled="true" >
to compress JSON in Web API responses. But judging by the content-length and content-type in the response header, IISExpress isn't compressing the response and therefore the config changes are not taking affect.
I also restarted IISExpress.
Any ideas? Thanks!