A Large Language Model is a neural network with billions of parameters trained on enormous text corpora to predict the next token in a sequence. The output looks like reasoning and conversation but is grounded in token-level statistical prediction. GPT-4o, Claude 3.5 Sonnet, and Gemini 2.0 are the dominant frontier LLMs in 2026.
LLMs power chat assistants, code completion, summarisation, and translation. Their main constraints are context window size, hallucination rate (when the model invents facts), and inference cost per token. The frontier model layer is dominated by OpenAI, Anthropic, Google, and Meta.