Disclosed embodiments are related to Application Programming Interface (API) technologies, and in particular, to Order APIs that are used to make modifications and cancelations to existing order objects. The Order APIs can be used to retrieve the current state of an order object, retrieve the summarized state of an order object as of a specified date, and retrieve a potential state of an order object along with specified changes. The Order APIs are also used to process order changes including changes to the quantity of an existing order object and applying line item changes to an existing order object. Other embodiments may be described and/or claimed.