Application interfaces are often subject to change during the development process.

New business use cases are included and existing one refined. The question is, how are these changes reflected in the API?

It depends on the nature and environment of the enterprise application how stable the API needs to be. If the project team is both in charge of the service, all clients and their life cycles, the API can introduce arbitrary changes that are reflected in the clients at the same time. The case is the same if for some reason the life cycles of involved applications are identical.

Usually, life cycles of distributed systems aren't that tightly coupled. For any other client/server model, or applications that have different life cycles, the APIs must not break existing clients. This means that the APIs are fully backwards-compatible, not introducing breaking changes.