If you read the documentation, I give an extended argument for why this is useful: it enables more object-oriented protocol design. http://kentonv.github.io/ca

If you read the documentation, I give an extended argument for why this is useful: it enables more object-oriented protocol design. http://kentonv.github.io/capnproto/rpc.html http://kentonv.github.io/capnproto/rpc.html Also, it is not the case that the new RPC's input type has to match the old one's output. You can take just one object embedded in the old response and use it in the new request. Please do look at the examples.