I've been building a tool that monitors how brands show up in ChatGPT, Gemini, Grok, and Perplexity answers. Most "GEO playbooks" I read assume the four LLMs behave roughly the same — same internet, same authoritative sources, optimize once, ship everywhere.

Wanted to test that assumption with actual data. So I sampled the same 5 prompts across all four models, four times each over 18 hours, and pulled every cited URL.

700 citations later, the four models barely overlap. The intersection of all four top-10 lists is exactly one domain ( visible.seranking.com ).…