What is schema evolution and deprecation strategy in GraphQL?

GraphQL's strongly-typed schema makes evolution both safer and more deliberate than REST. The core principle is additive-only changes: you can add new fields, types, and arguments without breaking existing clients (since clients only request fields they know about). Removing or renaming fields is a breaking change. The deprecation lifecycle uses the @deprecated(reason: "Use newField instead") directive to signal that a field should not be used in new code. Monitoring tools (Apollo Studio) track deprecated field usage by client — only remove a deprecated field after all clients have migrated (usage drops to zero). For argument changes, add new optional arguments rather than modifying existing ones. Schema registries enforce this lifecycle: CI pipelines run schema check commands that fail if a proposed schema change would break any registered client query.