On Lufthansa, most "revenue" booking classes are upgradeable, but the cost and method depend heavily on the specific letter code. Generally, for Economy to Business upgrades, classes like Y, B, M, U, H, X, Q, and V are the most flexible for mileage or voucher upgrades. Deeply discounted "Light" fares (often class K, L, or T) were historically restricted but can now often be upgraded via "Fixed Price Upgrades" during online check-in, provided there is availability. For those using Miles & More or Star Alliance points, the most expensive tickets (Y and B) require the fewest points. It is important to note that "Group" bookings or tickets issued by other airlines (codeshare) may have more restrictive rules. In 2026, the best way to check is via the "My Bookings" section on the Lufthansa website, which will display real-time "Offer-based" or "Fixed-price" upgrade options tailored to your specific ticket.