API Gateway's three API types (REST, HTTP, WebSocket) are not merely a matter of feature differences — they implement fundamentally different networking paradigms. REST API and HTTP API are built on the request-response model of HTTP/1.1, while WebSocket API implements the persistent bidirectional connection of RFC 6455 (the WebSocket Protocol). Which API type you choose is an architectural design decision, and choosing wrong means either 70% wasted cost or real-time features that are fundamentally impossible. In this file we dissect the WebSocket API's connection lifecycle and how HTTP API differs from REST API at the level of internal behavior.