To run an experimental workload on an EC2 instance continuously for up to 12 hours and then stop it, which EC2 purchasing option is the most cost-effective?

On-Demand Instances are the most cost-effective for this scenario because they offer pay-as-you-go pricing without long-term commitments, ideal for short-term, experimental, or unpredictable workloads. You only pay for the compute capacity you use, by the second, with no upfront costs. Reserved Instances are designed for steady-state, predictable workloads with a commitment of one or three years, making them unsuitable for a 12-hour experimental run. Spot Instances are for fault-tolerant workloads that can tolerate interruptions, as AWS can reclaim them with short notice, which is not ideal for a continuous 12-hour experiment. Dedicated Instances provide instances on single-tenant hardware for regulatory or licensing needs and are significantly more expensive, offering no cost benefit for this use case.