Which Amazon EC2 pricing option can provide cost reductions of up to 90%?

Spot Instances offer the largest cost savings, up to 90% compared to On-Demand prices, by allowing you to bid on unused EC2 capacity. However, they can be interrupted with a two-minute warning if EC2 needs the capacity back. Reserved Instances provide significant discounts (up to 75%) for a committed term (1 or 3 years) but are not as flexible or deeply discounted as Spot Instances. On-Demand instances are the most expensive but offer flexibility with no long-term commitment. Dedicated Hosts provide physical servers for your exclusive use, which can be costly but are useful for specific licensing requirements.