Nate Sullivan

I’m a solo founder and senior iOS engineer specializing in AI-native consumer products. I build systems that generate real content end-to-end—scripts, audio, and delivery—while staying profitable through subscription economics and unit-cost control.

I created Castify, an AI-generated podcast app that researches source material, writes scripts, generates audio, and delivers listenable podcasts in seconds. I handled production iOS with Swift/SwiftUI and AVFoundation/AVAudioEngine, and I integrated multiple LLM and media providers (OpenAI, Anthropic, Groq, Cerebras, Whisper, ElevenLabs, Fish Audio) using multi-provider switching for cost and latency.

When viral demand spiked—17.8M TikTok views and 100x traffic pressure—I rewrote the inference pipeline in three days (caching, batching, provider switching) to keep the app up and keep unit economics positive. Castify is live with 70,000+ lifetime downloads, paying users in 50+ countries, content in 70+ languages, and $80,000+ in lifetime revenue.

Before going all-in, I worked in a regulated bank environment as a Data Associate, managing SQL analytics and reporting tied to a $1B+ deposit insurance fund exit. That background shows up in how I ship: rate limiting and abuse prevention with SQL, analytics with Mixpanel funnel/milestone tracking, and disciplined product iteration—from A/B testing to subscription paywall design.