What is…
Context window
How much text a model can 'see' at once — your conversation, files and instructions, all measured in tokens.
The context window is the model's working memory for a single conversation. Everything counts against it: your messages, its replies, pasted documents, uploaded files, and hidden instructions. Modern models range from roughly 100,000 to a million-plus tokens.
When a conversation outgrows the window, older material gets dropped or summarized — which is why very long chats can 'forget' what you said at the start. Starting a fresh chat for a new task is one of the simplest quality upgrades there is.
💡 Think of it like
A desk. A bigger desk holds more papers at once, but a cluttered desk still makes it harder to find the one that matters.
📌 Example
A 200K-token window fits roughly a 500-page book.
🧠 Test yourself
Which of these describes Context window?
Related terms
Token
The chunk of text a model actually reads and writes — roughly ¾ of a word on average.
RAG (Retrieval-Augmented Generation)
Looking up relevant documents first, then having the model answer using them — grounded, current, citable.
Context engineering
Deliberately choosing what goes into the model's context — instructions, files, examples, tools — to get reliable results.
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