Context Window
Also: context length, token limit
The context window is how much text Claude can hold in its attention at once — your conversation history, any documents you've shared, system instructions, and Claude's own responses. Once you hit the limit, older content gets pushed out. Claude 3.7 Sonnet has a 200,000-token context window, which is roughly 150,000 words. Long contexts let Claude analyse full documents or maintain long conversations — but they also cost more and can sometimes cause Claude to lose focus on earlier material.
In practice
You paste a 200-page document into Claude and it reads the whole thing. You paste a 1,000-page document and it can only see part of it. The context window is the maximum amount of text Claude can hold in mind at once — everything in one conversation. Longer context windows mean Claude can work with bigger documents and longer conversations without forgetting earlier parts.
Related concepts
Where Context Window shows up
5 articlesThe context window shapes what Claude can and can't do in any given conversation. Here is how to work with it.
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200,000 tokens sounds enormous. In practice, how you use that space changes everything about the quality of your outputs.
Context window is the single number that shapes everything about how Claude thinks with you — and most people are using only a fraction of it.