Context window.

The context window is how much your AI can hold in its head in one chat before it loses the plot. Picture a bar that fills up as you talk. Every message, every file, every tool result takes up a bit more room.

The cleanest way to think about it is onboarding a new hire. Tell them too much at once and they start forgetting the first things you said.

Past about 50% of your context window used, that's when you start getting Hallucination and the quality drops. The good news is the windows got huge. The top models jumped from 200K to 1M Tokens, so you've got far more room than you used to.

The move is still to keep your main chat clean for the actual thinking and decisions, and push the grunt work somewhere else. A cluttered context is the number one reason a session quietly goes downhill.