Netflix recently migrated their mobile apps to GraphQL with zero downtime. This was a major undertaking, as it involved a total overhaul from the client to the API layer.
The team used a technique called Federated GraphQL, which allows domain teams to independently manage and own specific sections of the API. This made it easier to migrate the apps, as each team could focus on their own area of responsibility.
The migration was a success, and Netflix is now able to take advantage of the many benefits of GraphQL, such as improved performance, scalability, and flexibility.