How do you use OpenAPI in an ASP.NET Core API beyond just showing Swagger UI?

In production I generate the specification deterministically in CI and compare it with the released version for breaking changes. I verify required and nullable fields, enum behavior, content types, authentication schemes, pagination metadata, ProblemDetails responses, and every meaningful status path. Generated clients are tested against a deployed contract rather than assumed correct from schema generation alone. Internal models and sensitive fields are excluded through explicit DTOs, while examples avoid real secrets or personal data. Versioned specs are published alongside the matching service version, and exceptions to compatibility checks require an owned migration plan instead of silently accepting drift.