What is Context window?
How much text an AI model can keep in mind at once — your conversation, uploaded files and its own replies combined.
Everything in a chat — your messages, the AI's answers, pasted documents — has to fit in the model's context window. When a conversation grows past it, the oldest parts are dropped or summarised, and the AI starts “forgetting” earlier instructions.
Bigger context windows let you upload whole books or long PDFs, but very long inputs can still make answers less precise. For important work, restate the key instructions near the end of your message.
Practical tip
If a long chat starts ignoring your style rules, open a new chat and paste a short summary plus the rules at the top.
Related terms
The small chunks of text an AI model reads and writes — roughly a word or part of a word. Limits and pricing are counted in tokens.
The type of AI behind chatbots like ChatGPT, Gemini and Claude, trained on huge amounts of text to predict and generate language.
A technique where the AI first looks up relevant documents and then answers using them, so replies are grounded in real sources.
