GCP API Gateway vs Cloud Endpoint
Both API Gateway and Cloud Endpoint are used to manage your APIs: you create APIs to be hosted on GCP and to be consumed by others.
API Gateway is a relatively new offering (still in beta as of 2020).
The key difference is that API Gateway (based on Envoy) is fully managed by Google, while you need to manage your own Cloud Enpoint: Google just provides a software package called Extensible Service Proxy (ESP) (v1 based on NGINX and v2 based on Envoy) and you need to deploy it.
API Gateway reduces the complexity of deploying and managing APIs, and it is comparable to Amazon API Gateway and Azure API Management. I would not be surprised if Cloud Enpoint is deprecated some day.