The Week Without ChatGPT Attribution
Starting October 9, ChatGPT suddenly stopped tacking “utm_source=chatgpt.com” onto the links included in the model’s responses, and just like that, the traffic-tracking worlds of SEO and GEO professionals was thrown into a tizzy.
Instinctively, those watching their sites’ referral traffic nosedive feared ChatGPT users were genuinely clicking to their sites less.
Cedric Huesler, senior director of product management for brand visibility solutions at Adobe, tracked 500 webpages that lost 31,000 visits per day from ChatGPT referrals week-to-week for the week starting October 9. However, closer inspection showed direct traffic increased 26,000 visits per day on the same pages - signaling the change was in attribution, not in traffic.
The attribution change overlapped ChatGPT’s rollout of GPT-6 and Intelligent UI.
ChatGPT has not publicly commented on the incident, but Huesler has said ChatGPT confirmed to him that the issue was a bug with a fix imminent that will restore the use of the UTM in ChatGPT’s links.
For marketers, the week has been another exciting episode in the fast-changing world of LLMs. Stay abreast of the latest model changes with Evertune’s model tracker and research into models’ evolving behaviors.
Methodology
At Evertune, we track thousands of brands across LLMs by running millions of prompts a day. For this analysis, we reviewed more than 25,000 ChatGPT responses for prompts run multiple times a day from Sept. 15-Oct. 15, 2026.
Evertune is the first Generative Engine Optimization (GEO) platform built to explore, measure, act and advertise across the entire AI customer journey, connecting brands directly to ChatGPT Ads and programmatic advertising partners like The Trade Desk and Index Exchange. Where most GEO tools sample each prompt once a day, Evertune samples every prompt 100 times per model across 11+ AI models, delivering statistically significant visibility data at half the cost of competing platforms. Evertune's agents do the work for you: a prompt agent mines over 150 million real user conversations to find the exact questions buyers ask, an insights agent tells you what to do next each week, and an ads agent builds a complete ChatGPT campaign around your visibility gaps. From there, Evertune closes the loop with website optimization, data-driven content creation, source-level influence mapping and paid activation through affiliate and programmatic AI retargeting partners. Founded by the team that pioneered programmatic advertising at The Trade Desk, now building the next marketing channel.
