AI Glossary
What is a context window?
Context window: The context window is the maximum amount of text — measured in tokens — that an AI model can "see" at once in a conversation.
In plain English
Picture a desk of fixed size. Everything you and the model have said sits on the desk; when it fills up, the oldest papers slide off the edge. The model isn't being forgetful out of laziness — text outside the window simply does not exist for it anymore.
Why it matters
- Explains why long chats "drift" and forget early instructions
- Determines how much of a document you can paste at once
- Bigger windows cost more to run — there is always a limit
A concrete example
If a model has a 128k-token window (~300 pages), pasting a 500-page contract means the first 200 pages are invisible to it — silently.
Related terms
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