We shipped an AI-powered iOS chat app in 8 weeks. Here is what we learned about SwiftUI, OpenAI, and app store submission.
By David Friedman, Founder of AppBrewers
Conversify is an AI chat app for iOS that we built to explore the intersection of mobile UX and large language models. The project took 8 weeks from concept to App Store. Here are the technical and product lessons.
Tech Stack
| Layer | Technology | Why |
|---|---|---|
| UI | SwiftUI | Native iOS feel, fast iteration |
| State | SwiftUI @State + Combine | Built-in reactivity |
| AI | OpenAI GPT-4o | Best reasoning quality |
| Backend | Firebase Cloud Functions | Serverless, scalable |
| Auth | Firebase Auth | Apple Sign-In support |
| Storage | Firebase Firestore | Real-time sync |
| Analytics | Mixpanel | User behavior insights |
Key Technical Decisions
1. Streaming Responses
Users expect instant feedback. We implemented server-sent events for token-by-token streaming.
Challenge: SwiftUI lists re-rendering on every token caused UI jank.
Fix: Batched tokens in 50ms windows and used diffable data sources.
2. Conversation Persistence
Storing conversation history locally + syncing to Firestore.
Challenge: Large conversations (100+ messages) caused slow queries.
Fix: Pagination + local caching with Core Data.
3. Context Window Management
GPT-4o has a 128k token limit. Long conversations need intelligent context summarization.
Solution: Summarize older messages every 20 turns, keeping only recent messages verbatim.
App Store Submission Tips
- Test on physical devices (simulators miss performance issues)
- Prepare screenshots for all iPhone sizes
- Write clear app descriptions with keywords
- Have a privacy policy ready
- Be ready for rejection round 1 (it is normal)
What We Would Do Differently
- Start with UI tests from day one
- Use MVVM + coordinators instead of view-level state
- Implement offline mode earlier
- Add push notifications for async AI tasks
Timeline
| Week | Milestone |
|---|---|
| 1-2 | Design + SwiftUI prototypes |
| 3-4 | Core chat + OpenAI integration |
| 5-6 | Persistence + auth + polish |
| 7 | Testing + beta (TestFlight) |
| 8 | App Store submission + launch |
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Originally published on the AppBrewers Blog.
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