The context window number in your model's docs is a capacity spec, not a promise. A model that advertises 200K tokens will happily accept 200K tokens, but the quality of what it does with them starts sliding long before you reach that ceiling. If you build production features assuming the whole window works equally well, you will ship bugs that only show up on long inputs. Here is how token budgets actually behave, and how to stop the window from quietly lying to you. The number on t...