ChatGPT holds an 80.5% implied probability of topping the US free App Store chart on September 18, reflecting traders' assessment of its consistent user engagement driven by ongoing large language model enhancements and broad AI feature adoption. Competing apps such as Vinted, Muse, and Polymarket sit well below 10%, underscoring limited near-term momentum against the established chatbot's ecosystem integration and developer updates. Google Gemini and Google Maps trail further at under 2%, consistent with historical patterns where AI-native experiences outperform mapping or search utilities in short-term ranking spikes. With resolution just two days away, any last-minute app store algorithm shifts or unannounced releases remain the primary swing factors in this closely watched outcome.