A large language model is a neural network trained on massive text datasets to predict and generate human-like text. LLMs power all modern AI coding tools, from inline autocomplete to autonomous agents.
The major LLM families used in coding tools include GPT (OpenAI, used by Copilot), Claude (Anthropic, used by Claude Code), Gemini (Google), and various open-source models like Llama and Mistral.
Model size, training data, and fine-tuning determine what a model can do. Larger models with code-specific training generally perform better on complex programming tasks, but smaller models can be faster and cheaper for routine completions.