Archera Guaranteed Reserved Instances (GRIs) have two variable components, a term length and a Premium, that are inversely related. The longer the term length, the lower the premium, and vice versa - shorter term lengths have higher premiums. The GRI Premium is the difference between the standard 3 year RI Savings Rate, and the net savings rate of the GRI. This is represented in the Purchase Planner by clicking "View Details" under any plan:

Keep in mind, GRI premiums are only assessed on realized savings. Meaning - if for some reason you can't use the underlying infrastructure, you aren't responsible for the premium.