In September someone asked r/SEO whether ChatGPT uses Google's index or Bing's, and the replies disagreed. We tested it on October 19, 2026. We took 38 keywords across software, shopping, how-to and brand searches and searched each one on Bing and on Google from the same browser, set to US English. Then we ran the same keywords through ChatGPT's web app, using a data provider's live feed, and recorded every site it cited.
ChatGPT searched the web for 26 of the 38 keywords. It answered the other 12 from memory, mostly how-to and what-is questions. For the 26 it searched, it cited 147 different sites. For each cited site we checked whether it sat on page one of Bing or Google for that keyword. 25% were on Bing's first page and 24.5% on Google's. 10% were on both, and 60.5% were on neither. ChatGPT cited the site in Bing's first spot for 7 of the 26 keywords and the site in Google's first spot for 11.
The overlap changed with the kind of search. Brand searches like "asana vs monday" lined up best, with 37% of cited sites on Bing's first page and 33% on Google's. Shopping searches like "best air fryer" came in at 28% and 24%. Software searches like "help desk software" were lowest, 17% on Bing and 20% on Google.
One reason the numbers are low is that ChatGPT rewrites a keyword before it searches. For "best crm for small business" it searched "best CRM software for small businesses 2026 pricing features comparisons," and of the nine sites it cited, just one was on Bing's first page. We call the distance between the keyword you track and the search ChatGPT actually runs the rewrite gap.
So Bing rank tracking is a fair early signal and a weak stand-in for checking ChatGPT directly. This was one run of 38 keywords on one day, so treat the percentages as a pattern and not a stable rate.
RankControl, an AI SEO and AEO platform, ran the test. RankControl's AI visibility tracker tracks citations across 7 AI engines, so you can see what ChatGPT cites for your own keywords instead of inferring it from Bing. The full numbers, including the keyword types, are in the full write-up on Medium.