How do you design a reactive architecture in iOS using Combine at scale?

A scalable reactive architecture uses Combine publishers, centralized state, and strict separation between streams and UI.

At scale, Combine-based architecture typically enforces unidirectional data flow where ViewModels expose publishers (state streams) and accept inputs via subjects. Business logic is isolated in use cases, while networking and persistence feed reactive streams. The system avoids shared mutable state by relying on immutable state emissions. Proper cancellation handling and backpressure control are critical to prevent memory leaks and performance degradation.