How Large Language Models Search, Retrieve and Answer with Real-Time Web Data: A Reproducible Prompt-Chunk Fit Methodology for Generative Engine Optimization

Assistants like ChatGPT, Gemini, Claude, and Perplexity answer more and more of the user's questions by mixing what they learned in their training with what they can pull from the live web. Some studies estimate that around 70% of ChatGPT prompts express intents classic search never saw, and a third to a half of prompts trigger a live web search. For a brand, a publisher, or an institution, that changes priorities and sets a new course of action. Your page rank is becoming less important. What decides whether you are recommended in an answer is whether a specific fragment of your content gets retrieved, matched to the question, and used to compose the reply. This paper walks through that pipeline end-to-end: how a model reads intent, decides whether to search, plans queries, crawls or looks up in an index, extracts fragments, chunks and tokenizes them, turns them into vectors, matches them against the question, and finally writes the answer. Then it proposes a way to measure the whole thing and explains how you can help these systems provide better answers, especially when they talk about your brand. The key move is to stop treating the domain as the unit of analysis and start treating the relationship between prompt, chunk, model, and answer as the unit of analysis. There is strong resistance to abandoning SEO concepts and measurements when working with LLMs, but the evidence for this strategic shift is overwhelming. I propose a composite prompt-source fit score, and I do link it to metrics the retrieval community already knows: nDCG@10, precision@k, recall@k, mean reciprocal rank, and semantic similarity measures. The objective is to set a clear measurement discipline for Generative Engine Optimization (GEO). This approach should hold up under review and can be repeated across models, markets, product types, industries, and customer personas. Don't get me wrong: there are many details to discover; I still have many questions, data to validate, and the constant feeling that things keep changing as we speak. But these systems have affected us to the point that we cannot afford not to act immediately, so we need to understand how they work to improve their performance.