Larger windows let a model reason over more at once, but every token sent adds cost and latency, and relevant information can still be diluted by irrelevant text. This is why retrieval (RAG) stays valuable even as windows grow: it puts only the relevant passages in the window.
Glossary
Context window
A context window is the maximum amount of text, measured in tokens, that a language model can consider at once — its prompt plus everything generated so far. Anything outside the window is invisible to the model.