Google Analytics 4's new AI Assistant channel, added on May 13, 2026, and rolled out to most properties by early June 2026, undercounts AI traffic because it fragments a single source across multiple channels. The same source, chatgpt.com, can appear in three different channels: chatgpt.com / ai-assistant lands in AI Assistant, chatgpt.com / referral lands in Referral, and chatgpt.com / (not set) lands in Unassigned. This happens because GA4 decides the channel using source and medium together, not source alone. The list of platforms Google recognizes also changes; at launch it named ChatGPT, Gemini, and Claude, but by June the live documentation listed ChatGPT, Gemini, DeepSeek, Copilot, and Grok, with Claude dropped and Perplexity still not on the list. Similarweb’s clickstream data has ChatGPT referrals converting at around 7%, ahead of organic search and not far behind paid.