Context window is the memory of an ai.

Let’s say you open a new chat with ai and say tell me a story.

The ai responds with a story. You then ask it to continue the story.

This entire chat history is continuously resent to the ai to run through as if it all one text file. Your system prompt (typically “you are a helpful agent….”) and all other “context” given to the ai. So as your conversation gets longer you use more and more context until you start a new chat. Because the entire context is processed at once as if it all was a new chat, it gets slower and slower as the context fills up.

Gemini context window can hold 1M tokens , compared to most models that have 128k-200k this is huge, roughly 2.500 pages of text. This is a key demand of something like a d&d campaign that goes on for a very long period of time. You can’t restart a new chat and continue the adventure without feeding it the previous parts of the story. This is the main limitation of ai for story development, gaming, and things like movie writing.