We captured the network traffic of ChatGPT, Gemini and DeepSeek to see how each defines a "source" — they're three completely different mechanisms

Disclosure upfront: I'm the founder of an AI-visibility company, so this research scratches our own itch. Our domain was excluded from all counts before analysis. Not linking anything in the post. We wanted to answer a simple question: when an AI assistant shows you "sources," what is that, technically? So we opened devtools on the web clients of ChatGPT, Gemini, and DeepSeek, and ran the same 4 queries 10 times through each system. What we found: ChatGPT streams the answer over SSE and attaches citations as url_citation objects with start_ix / end_ix — character offsets into the generated text (UTF-16 code units, so emoji and CJK break your parsing if you count bytes). A citation is bound to a specific fragment of the answer, not the answer as a whole. Gemini runs on Google's batchexecute/JSPB transport — protobuf-as-JSON-arrays where fields have positions, not names. Next to each cited URL there's a family of short obfuscated fields. Our working hypotheses (not confirmed by Google docs): rs ≈ reliability score for the domain, ls ≈ last-seen date, GK ≈ character range (functional analog of ChatGPT's offsets). The interesting part isn't the exact decoding — it's that Gemini ships internal per-domain trust signals alongside every source. DeepSeek is the most transparent: a plain search_results[] array attached to the sub-queries it decomposes your question into. No offsets, no hidden fields. And what they actually cite is just as different: ChatGPT favored arXiv + Wikipedia (one arXiv paper got cited in 10/10 runs), Gemini favors big SaaS/marketing domains and — fun detail — never cited a single Google property in our runs, DeepSeek lives on press-release wires and news aggregators, including Chinese-language sources the other two never touched. Bonus finding: we compared all of this against Google/Bing top-10 for the same queries. URL-level overlap: 3.3% (4 matches out of 120 SERP positions). All four matches were Bing-side. Google: zero. Caveats: 4 queries from one