In one sentence
An LLM is the text-prediction model that sits behind an AI assistant: GPT behind ChatGPT, Google Gemini behind the Gemini app, Claude behind Claude, and so on.
Which model powers which engine
Every major AI search engine is built on an LLM, sometimes with retrieval and tools on top.
- ChatGPT runs on OpenAI's GPT family.
- Google Gemini, Google AI Overview, and Google AI Mode run on Google's Gemini family.
- Claude runs on Anthropic's Claude family.
- Perplexity uses a mix of LLMs with its own retrieval layer.
- Microsoft Copilot is largely GPT-based.
- Grok is xAI's own model family.
Each engine has its own training data, fine-tuning, system prompt, and retrieval behavior. That is why the same buyer question produces different answers across engines. Tracking one engine is not a substitute for tracking all of them.
Why brands care
AI assistants now sit between buyers and the open web for a large share of research queries. OpenAI reported 900 million weekly active users of ChatGPT in February 2026. Google reported more than 2.5 billion monthly users of AI Overview. Anthropic reported more than 300,000 business customers of Claude, including eight of the Fortune 10.
If an LLM does not mention your brand when a buyer asks about your category, you are effectively not in the consideration set. The same answer might not appear twice: AI answers are stochastic, so a single snapshot is not enough.
Frequently asked
- Is ChatGPT an LLM?
- ChatGPT is a product built on top of an LLM, OpenAI's GPT family. The LLM is the engine. ChatGPT is the car around it.
- Do all AI engines use the same LLM?
- No. Different engines use different models, often with different fine-tuning and system prompts. Answers differ accordingly.
- What is the difference between an LLM and a chatbot?
- An LLM is the underlying model. A chatbot is the user-facing product wrapped around it, with retrieval, tools, and guardrails.
Sources: OpenAI (ChatGPT 900M WAU, Feb 27, 2026); Google I/O 2026 (2.5 billion monthly AI Overview users); Anthropic (300,000+ business customers of Claude, 2025).