Sensor Tower's State of AI 2026 report reveals that ChatGPT became the fastest mobile app to reach 1 billion monthly active users (MAU), hitting the milestone in May 2026. OpenAI's chatbot leads with over 1.1 billion MAU, ahead of Google Gemini (around 662 million) and Claude (around 245 million). However, ChatGPT's True Audience share fell below 50% for the first time in March 2026, standing at 46.4% by the end of May, with Gemini at 27.7% and Claude at 10.3%. Claude's True Audience surged 452% year-over-year in May, and its U.S. market share climbed from 4.4% to nearly 14%. ChatGPT, Gemini, and DeepSeek together account for nearly 90% of time spent in AI assistant apps in Q1 2026. ChatGPT users spend roughly 215 minutes per month on the platform. The report also highlights AI's impact on e-commerce: GenAI referral traffic to shopping websites increased across every major retail category between Q4 2024 and Q1 2026. In Computers & Consumer Electronics, the GenAI traffic share rose nearly fourfold. Retailers like Walmart and Target recorded GenAI referral shares above 1.5%.