ServiceStack’s HTTP Caching story has been greatly improved in v4.0.56 which transparently improves the behavior of existing ToOptimized Cached Responses, provides a typed API to to opt-in to HTTP Client features, introduces a simpler declarative API for enabling both Server and Client Caching of Services and also includes Cache-aware clients that are able to improve the performance and robustness of all existing .NET Service Clients – functionality that’s especially valuable to bandwidth-constrained Xamarin.iOS / Xamarin.Android clients offering improved performance and greater resilience.

For more details please refer to the v4.0.56 Release Notes: https://github.com/ServiceStack/ServiceStack/blob/master/docs/2016/v4.0.56.md#http-caching