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Google’s AI ecosystem (AI Overviews, AI Mode, Gemini) and ChatGPT use different ranking signals, trust different sources, and reward different optimization strategies. Peec’s 500,000-prompt AI Overviews study (full study, published 2026) names five differences, drawing on Peec’s earlier 30-million-source analysis:
  1. AI Overviews heavily promotes YouTube. Video content is a direct pathway into Google’s AI surfaces that ChatGPT does not offer — see YouTube in AI search.
  2. ChatGPT does not render JavaScript. JS-heavy sites (React, Vue) are unreadable to ChatGPT but readable to Google — a structural advantage for AI Overviews on JS stacks.
  3. ChatGPT uses Reciprocal Rank Fusion (RRF). It fans your prompt out into multiple sub-queries and combines results, so winning means appearing across many related queries, not ranking for one — see What is a query fan-out.
  4. Both ecosystems lean heavily on Reddit. The one consistent signal across both — see Reddit in AI search.
  5. Non-English markets are harder in ChatGPT. ChatGPT mixes English and local-language sources even for non-English prompts, while AI Overviews stays closer to the query language — see ChatGPT searches in English.
The two systems share some signals (Reddit presence, content quality, citations) but diverge enough that one combined strategy underperforms on both; the study recommends separate tracking and optimization per surface. Source: AI Overviews is the most undertracked AI search: 500,000 prompts show why, Peec (Tomek Rudzki), May 2026.