A computer-implemented method, operable on a device in a content delivery network (CDN), wherein the CDN delivers content on behalf of at least one content provider, the device implementing a content delivery (CD) service, the method includes, by the service on the device: receiving a request for a particular resource from a client; determining whether the client includes an optimization support mechanism; when the client includes an optimization support mechanism, providing the client with a first version of the particular resource, optimized, at least in part, for the capabilities of the client in combination with the optimization support mechanism; otherwise providing the client with either (i) an un-optimized version of the particular resource, or (ii) a version of the particular resource optimized, at least in part, for the capabilities of the client without the capabilities of the optimization support mechanism.