SEO Guidance Portability Breaks Down as LLMs Use Different Corpora, Crawlers, and Alignment Methods

The article argues that the long‑standing portability of SEO guidance across search engines has broken down in the LLM era because major providers use different corpora, crawlers, retrieval systems, and alignment methods. Shared standards like sitemaps, Schema.org, robots.txt, and IndexNow once allowed webmasters to optimize once for multiple engines, but LLMs now rely on proprietary data and distinct user agents. Google’s own SEO guidance still applies to traditional search but not to Gemini AI Overviews or AI Mode, which cite only a fraction of top‑ranked pages. The llms.txt file, once promoted by the SEO community, is not consumed by OpenAI, Anthropic, or Google, and is compared by Google to a deprecated meta‑keywords tag. Gemini 3 replaced 42% of cited domains and increased sources per response by 32%, yet AI Mode citations overlap only 13.7% with the top 10 in Google Search. Structured data remains important but is insufficient for AI citations, and the guidance that treating one engine’s rules as a universal map is risky. The article highlights that advertisers and webmasters must test AI search performance separately from traditional rankings. It concludes that the shared‑standards model that once enabled portable SEO guidance is no longer available at the same scale for LLMs.