The rule is simple: coursework in your declared subjects goes to Learn mode. Everything else — drafting emails, summarizing articles, brainstorming, planning your week, life admin — goes to Efficiency mode.
The classifier makes this decision automatically. If you type a homework question into Efficiency, the classifier catches it and redirects you to Learn with a friendly nudge. That's the intended UX.
If Efficiency ever misclassifies (a false positive), the tutor system prompt in Efficiency mode still refuses to solve declared-subject problems. This is defense-in-depth. Corner cases fall through to safety, not shortcut.
If you're on the free plan, Efficiency is disabled. That's not punishment — it's the pricing that reflects the cost. Efficiency mode uses Sonnet-class inference for every message; it's the largest single driver of our per-user cost. The Student plan ($12/mo) turns it on.