What is Context Window?
The maximum amount of text (measured in tokens) that a large language model can process in a single interaction. Everything the model "sees" during a conversation, including the system prompt, conversation history, retrieved documents, and its own responses, must fit within this window. Once exceeded, earlier content is lost.
My perspective
In practice
Context windows have grown fast (from 4K tokens to 200K+), but bigger is not always better. A huge context window filled with irrelevant information produces worse results than a small window with carefully curated context. The real skill is context engineering: deciding what goes in and what stays out. Understanding context windows is essential for designing RAG systems, agent workflows, and any production AI application.