What is Context window?

Context window, explained

Anything outside the context window is invisible to the model. Larger context windows let you include long documents or long conversations, but filling them with irrelevant text can still reduce quality and increases cost. For large knowledge bases, RAG is usually better than pasting everything in: it retrieves only the relevant passages. In long chats, assistants may lose track of early details as the conversation grows, so restating key facts helps.