Wundergraph Cosmo is an open-source platform for creating and managing federated GraphQL APIs. It provides a schema registry with proper validation and schema checks to avoid breaking changes and errors in merging individual service schemas into a single, cohesive API surface. The platform consists of different modules, including the Studio for user-friendly UI interaction, the Router for understanding the Federation specification, the Control Plane as the glue binding everything together, and the CLI for creating, updating, and deleting new schemas. Cosmo can be self-hosted via Kubernetes or opted for a managed option in the cloud. The schema registry allows teams to review all subgraphs of their federated graph, download individual schemas, and inspect directly the schema of specific subgraphs. Schema checks detect composability errors (merge is not possible) and breaking changes (merge is possible but client applications will break), providing detailed information for fixing issues. Cosmo also offers an AI-powered feature to automatically fix composition errors with OpenAI integration.