Demand Control in Hive Router

Hive Router now protects federated graphs from expensive operations with Demand Control, a cost-based security layer that assigns numeric costs to operations and rejects those exceeding configured budgets. It implements the IBM GraphQL Cost Specification with directives like @cost and @listSize, estimating operation expense before execution, and supports supergraph-wide limits (up to 5000 cost units) as well as per-subgraph budgets (as low as 200 units for expensive services).