> ## Documentation Index
> Fetch the complete documentation index at: https://docs.getcited.in/llms.txt
> Use this file to discover all available pages before exploring further.

# LLM

> Large Language Model — the AI models that power ChatGPT, Gemini, Claude, Perplexity, and Grok.

**LLM** (Large Language Model) is a type of AI model trained on vast amounts of text data to generate human-like responses to natural-language prompts. LLMs power the AI search platforms where brand visibility is measured — [ChatGPT](/concepts/platforms/how-chatgpt-search-works), [Perplexity](/concepts/platforms/how-perplexity-ranks-sources), [Gemini](/concepts/platforms/how-gemini-search-works), [Claude](/concepts/platforms/how-claude-search-works), and [Grok](/concepts/platforms/how-grok-search-works).

## Why it matters

LLMs are the "search engines" of AI search. Understanding how they generate responses — blending training data with optional live retrieval, exhibiting [non-determinism](/concepts/foundations/non-determinism), and preferring certain [source types](/concepts/foundations/ai-citation-sources) — is a prerequisite for effective AEO/GEO work. Each LLM has different behavior: ChatGPT uses Bing for retrieval, Perplexity always searches live, Claude relies more on training data.

## How Cited uses it

Cited tracks LLMs from OpenAI, Anthropic, Perplexity, Google, and xAI, each queried with the same set of consumer-authentic prompts. The full tracked set is documented in [Which AI platforms we track](/methodology/which-llms-we-track). Each LLM contributes independently to a brand's overall visibility picture.

## Related concepts

* [Which LLMs we track](/methodology/which-llms-we-track) — the specific models and rationale
* [Non-determinism](/concepts/foundations/non-determinism) — a fundamental property of LLMs
* [RAG](/glossary/rag) — how some LLMs augment training data with live retrieval