TL;DR: With around 800 million weekly users, 95% of whom are on the free tier, it's somewhat surprising that OpenAI has never introduced ads to its incredibly popular chatbot. But based on some newly discovered code, it appears that will soon change.
Copilot Mode in Edge turns the browser into an AI assistant that organizes sessions into "Journeys" and completes multi-step tasks like planning trips or managing subscriptions. With optional personalization via browsing history and a focus on privacy, Copilot Mode is clearly Microsoft's reaction to ChatGPT Atlas.
Atlas is OpenAI's new web browser built on Chromium, with ChatGPT integrated into the browsing experience. It offers instant page summaries, inline editing, and an optional memory system that personalizes what you see and how you work. Agent Mode (in beta) can take actions for you. Atlas is available now on macOS, with Windows, iOS, and Android versions on the way.