Non-Authoritative Information

The returned metadata is from a copy, not the origin server.

203 Non-Authoritative Information means the request succeeded, but a proxy between you and the origin transformed the response, so what you received isn't byte-for-byte what the origin sent. Think of a proxy that recompresses images or rewrites markup. In practice it's rare: most transforming proxies just pass along a 200 without admitting to the changes.

GET /news/latest HTTP/1.1
Host: example.com

HTTP/1.1 203 Non-Authoritative Information
Via: 1.1 corp-proxy.example.net
Content-Type: text/html