I wanted to know how Duolingo makes money on Android -- ads vs Super subscription, which SDKs they use, and how aggressive the free tier is. So I decompiled Duolingo 6.79.5 (164 MB APK, 11 DEX files, 242 activities). TL;DR IronSource mediation sits at the center -- Unity Ads, Vungle, Moloco, AdMob, Facebook, and Pangle all plug in around it Facebook Audience Network ships as a 5 MB hidden DEX in assets (same trick as CamScanner) 7+ ad networks for free users; Google Play Billing for Super/Plus (no RevenueCat found) Kotlin + Jetpack Compose for the main app; Unity for some game modules (chess, etc.) Staging APIs ( android-api-stage , goals-api-stage-* ) are hardcoded in the production build Adjust + Sentry (+ Firebase) for attribution and crashes How Duolingo Makes Money Subscriptions (Super / Plus) Duolingo uses Google Play Billing directly -- ProxyBillingActivity , PlusPurchaseFlowActivity , strings for gems and family plans. Deep links hit duolingo.com/settings/super .…