What is LLM (Large Language Model)?
An LLM is a neural network trained on massive amounts of text that can generate, summarize, classify, and reason about language — GPT-4, Claude, Llama, Gemini.
Definition
A Large Language Model (LLM) is a neural network — usually a transformer architecture — trained on hundreds of billions to trillions of words of text. In 2026, the production-grade LLMs are GPT-4o (OpenAI), Claude 3.7 Sonnet (Anthropic), Gemini 2.0 (Google), and open-source families like Llama 3.3 and Mistral. LLMs are the "brain" of every modern AI agent — they understand instructions, generate responses, classify intent, summarize, and reason. Most production systems use multiple LLMs together: a cheap one (Claude Haiku, GPT-4o-mini) for classification + routing, and an expensive one (GPT-4o, Claude Sonnet) for complex reasoning.
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