What is Schema Stitching vs Apollo Federation?

Both are patterns for combining multiple GraphQL APIs into a single gateway, but they operate differently.

Schema Stitching is an imperative approach where you write code at the gateway to manually map and combine schemas and resolve cross-service links. Apollo Federation is a declarative approach; the subgraphs use directives (like @key) to define how they share entities, and the Gateway automatically composes the supergraph and routes queries.