Definition
Context Window
The context window is everything the model can see for a single request: system prompt, conversation history, retrieved documents, tool schemas, and tool results. The book's mental model is that the LLM is a CPU and the context window is its RAM; nothing outside it exists to the model. Windows grew from 512 tokens to over a million, but attention cost scales quadratically with length.
Explained in
Chapter 8: Prompt Engineering and Context Engineering
The number one practical skill for anyone working with AI.
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