The chat.
The chat is what you've said in this conversation, plus what Claude has said back. It resets when the chat ends. This is the layer everyone uses by default — and the layer everyone over-uses, because they don't know the other three exist.
// What belongs here vs. doesn't- The task — what you want done right now
- The input — the document, data, draft you're working with
- Task-specific length and format — "in 200 words", "as a table"
- One-off context — the specific audience for this output
- Your role and standing context — that's Layer 2 or 4
- Your writing style preferences — that's Layer 2
- Reference documents you reuse — that's Layer 3
- Facts about you Claude should remember — that's Layer 4
About 80% of that prompt is the same thing you'd type next time. The role, the firm context, the style rules, the spelling, the "don't guess" rule — they're all standing context. Only the task, the document, and the specific audience are genuinely one-off. That's the case for moving the rest into Layers 2, 3, and 4.