Amazon Relational Database Service (Amazon RDS) now supports C6gd database (DB) instances in RDS for PostgreSQL and MySQL Multi-AZ deployments with two readable standbys. These compute optimized DB instances are available in sizes ranging from 1 vCPU up to 64 vCPU (medium up to 16xlarge sizes). C6gd DB instances are the only instances that support medium size instances for Multi-AZ deployments with two readable standbys. C6gd is an ideal candidate for cost optimizing dev/test workloads intended for Multi-AZ deployments with readable standby instances.
Source:: Amazon AWS