This is widely considered the "sweet spot" for maximum value. Booking this far out allows you to secure highly sought-after Explorer Suites and Veranda Suites before they sell out.

While rare for river cruises, occasional deep discounts may appear for unsold cabins. However, this often results in limited cabin choices and potentially higher airfare costs. Seasonal & Promotional Opportunities

Viking maintains a predictable cycle of promotions that can further reduce your costs: Best time to book Viking cruise? - Facebook