Oh, I assumed coordinators served blocks to clients. This makes more sense.
There are two APIs: * Coordinator: the API for coordinating coinjoins and collaborative transactions and * Backend: the API for providing filters, fee estimations, exchage rates, etc. The coordinator API is run by random volunteers while the backend was run by zkSNACKs until a few hours ago. Soon, we won't run any infrastruture and we hope multiple friends/freedom fighter help us by hosting a backend API.