Discuss Performance Implications of Abstract Types (Unions/Interfaces).

Resolving abstract types requires the server to determine the concrete type at runtime, adding computational overhead.

When a resolver returns an Interface, GraphQL executes an internal __resolveType function to check the object's shape and assign the correct type so it knows which fields to validate. In highly polymorphic lists (e.g., returning 10,000 feed items of mixed types), this reflection-like checking can bottleneck the CPU.