Definition
A large language model (LLM) is an AI model trained on broad data that generates text by predicting what comes next. The most citable formal wording, published by NIST in 2024, describes a model trained on broad data, generally using self-supervision, containing at least tens of billions of parameters.
Example. ChatGPT is the product. GPT is the model underneath it. Gemini is a model, and Google's AI Mode is one place that model is used.
You can test what these models say about your brand with the free AI Visibility Tester.
What is the difference between a model and the product using it?
The difference is that a model generates the text and a product decides what the model is given. It matters commercially, because the product is where your content enters the picture. The same model answers differently depending on whether the product searched the web first.
| The model | A product built on it | What that product adds |
|---|---|---|
| GPT | ChatGPT | A chat interface, plus web search when the question needs it |
| Claude | Claude apps and Claude Code | Tools, files and the ability to run work on your own machine |
| Gemini | Google AI Mode | Google Search retrieval, with links out to sources |
Why does an LLM go out of date?
An LLM goes out of date because training ends on a date and the world does not. Anything after that date is missing unless the product fetches it at the time of the question. That is the whole reason retrieval exists, and retrieval only reaches pages the search bots are allowed to fetch.
What is a context window?
A context window is the amount of text a model can hold in mind at once, counted in tokens rather than words. Anthropic documents a one million token window on its current Claude models, which it puts at roughly 555,000 words. Anything past the window has to be summarised or dropped.
What do people get wrong about LLMs?
- Treating a model name as a product name. Blocking one product's crawler does nothing about another product on the same model.
- Assuming a confident answer is a retrieved one. An answer with no link is usually memory, not research. That is where an AI hallucination lives.
- Citing NIST for a definition. NIST has no glossary entry for large language model. The wording above comes from a 2024 NIST publication quoting an executive order that has since been revoked.
Mentioned in
Sources
- NIST AI 600-1: Generative AI Profile (July 2024)
- Anthropic: Claude model overview and context windows
Last checked against these sources on 23 September 2026.