What is a context window?
A context window is the maximum amount of text, measured in tokens, that an AI model can consider at one time, including your messages, any documents you paste, and its own replies. Anything beyond the window is dropped, so the model effectively forgets it.
How does a context window work?
Each time you send a message, the app sends the whole recent conversation to the model again. When it gets too long, the oldest parts are cut or summarised to fit the window.
Why does a context window matter?
It explains why long chats drift and why the AI 'forgets' early instructions. Bigger windows let you work with long documents, but cost more.
An example
Example: Paste a 200-page tender document into a chatbot with a small context window, and it can only use the parts that fit.
Related terms
Learn it properly
A context window is covered in AI Builder, with short lessons, practice questions and instant feedback.