Only 11% of domains cited by ChatGPT and Perplexity for similar queries overlap (2026 market data). It's not a measurement error: it reflects real differences in how the two engines find and evaluate sources.
Why this happens
- Different grounding sources: Perplexity relies heavily on a real-time web search index with explicit citations; ChatGPT, when browsing, relies on a different engine (Bing/OAI-SearchBot) with its own ranking logic.
- Different training data: each model's "base" knowledge (before browsing) comes from different training corpora, gathered at different times with different crawlers (GPTBot vs ClaudeBot vs CCBot).
- Different synthesis criteria: each engine weighs "authoritative but generic source" against "specific but less known source" differently — there's no single shared ranking.
What this means for your strategy
Optimizing for a single engine (even the most popular one today) leaves a huge share of queries on the others uncovered. A site that's technically solid on all the baseline signals (bot accessibility, schema, structure) is more likely to get cited everywhere, because those signals are necessary conditions shared by all engines — not sufficient on their own, but without them you're not in the running on any of the four.
How to check this for your brand
Multi-engine prompt tracking (AIVIS dashboard) runs the same prompts across OpenAI, Perplexity, Gemini and Claude and shows the differences side by side — it's the only way to know whether your slice of that 11% overlap includes you or excludes you.