The document discusses Greenfield API, a new full API layer for BTCPayServer that allows managing BTCPayServer entirely through code. This would enable headless BTCPay and allow third parties to build applications that enhance and extend BTCPay's functionality. Examples of potential uses include exchanges automatically configuring stores for each user or integrating and extending BTCPay with external applications. The API will use OpenID for authentication and REST and SignalR for interfacing.