Context Window

Definition

The context window is the maximum amount of text (measured in tokens) a model can see in one request at once — your messages, any uploaded files, the conversation so far, and the response, all combined.

A useful picture

Imagine a desk. No matter how smart you are, you can only work with what's on the desk right now. Everything in the filing cabinet next to it stays invisible unless you put it on the desk too. The context window is the size of that desk.

Why it matters

If a conversation or a file is too long, it won't all fit. Older messages or parts of the file get pushed out or need to be summarized. The AI effectively "forgets" them — not because it's careless, but because there's no room left.

Practical tip

In long chats or large codebases, it helps to share only the relevant snippets instead of everything at once. Some agents automatically summarize older parts ("compaction") to free up space.