Tokens & Context Windows, Explained Simply
The context window is the single most useful concept for making sense of why a model “forgets” the start of a long chat or suddenly gets pricey. This guide is for builders who want to stop guessing and start estimating — what a token is, how the context window bounds the model’s memory, what happens when you overflow it, and how it all maps to cost. In this guide What a token is Why models count tokens, not words The context window: the model's short-term memory What happens when you run out Tokens and cost Estimating tokens quickly Practical tips to fit more in FAQ Quick answer: A token is a small chunk of text (about four characters of English), and the context window is the maximum number of tokens a model can consider at once — your input and its reply combined. Go over that limit and the oldest text falls out of view. What a token is A token is the unit a model reads and writes — usually a short chunk of text rather than a who...