Used [fiddler][1] to double-check<sup>*</sup> this.

Everything I get back from the API is definitely gzip compressed.

For that matter, you can't get a response that isn't compressed; you can only choose between gzip & deflate.  Default is gzip.

The API always sets the `Content-Encoding` response header, so you might be the victim of your library decompressing the response for you.

<sub>*Triple-checked: I ran our test cases without setting `Accept-Encoding` but leaving the gzip decompression code in.</sub>

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Bare minimum request using the world's worst stackoverflow clone (w/ gzip off):

Header:

    GET http://api.stackoverflow.com/0.8/users/242897/comments/160173?sort=votes&order=desc&page=1&pagesize=30&key=iv1qWOxcwkaKg53RJIXh-A HTTP/1.1
    User-Agent: WorldsWorstStackOverflowClone
    Host: api.stackoverflow.com
    Connection: Keep-Alive

Response:

    HTTP/1.1 200 OK
    Server: nginx
    Date: Sun, 13 Jun 2010 13:44:21 GMT
    Content-Type: application/json; charset=utf-8
    Connection: keep-alive
    Cache-Control: private
    Content-Encoding: gzip
    X-AspNetMvc-Version: 2.0
    X-RateLimit-Max: 10000
    X-RateLimit-Current: 9473
    X-AspNet-Version: 2.0.50727
    Content-Length: 625
    
    [gzip'd byte stream]

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This is a quite old question, but just to be 100% clear.

The API **always** responds with gzip'd content.

There are cross policy domain files on the API, StackAuth, and sstatic for Flash **and** Silverlight.

  [1]: http://www.fiddler2.com/fiddler2/