Client-side endpoint configuration can be accomplished by allowing a client to include as part of an API request, a desired endpoint for subsequent notifications from a server. The endpoint can be an endpoint identifier, such as a Uniform Resource Identifier (URI) or a domain name. When a web service receives the API request from a client device, the web service can generate a response to the request and send the response to the endpoint identified in the request. The API request can asynchronously communicate with the client device whenever the response is completed.