How do Amazon EC2 Reserved Instances that are regional or size flexible work?

All EC2 Reserved Instances that are size flexible also provide the regional benefit, but the reverse is not always true.

For a Reserved Instance to provide the regional benefit, the following must be true:

• It must be a Standard or Convertible Reserved Instance.
• It must be in the active state.
• It must not be tied to a specific Availability Zone.

For a Reserved Instance to be size flexible:

• It must meet the regional benefit criteria.
• It must have a platform value of Linux/UNIX.
• It must not be a G4 instance.
  

A Reserved Instance that provides the regional benefit applies to any instance in that Region that matches the specifications of the Reserved Instance.

A Reserved Instance that is size flexible applies all or part of its pricing benefit to any instance in the same instance family, regardless of Availability Zone or size.

For example, a Reserved Instance that is size flexible for a c4.large instance applies to either a c4.large instance or two c4.medium instances. In the same way, two c4.medium instances can also be applied to usage for a c4.large instance.