Today, we are announcing the availability of Optimize CPUs for Amazon EC2 instances. This feature provides customers greater control of their EC2 instances on two fronts. First, customers can specify a custom number of vCPUs when launching new instances to save on vCPU-based licensing costs. Second, they can disable Intel Hyper-Threading Technology (Intel HT Technology) for workloads that perform well with single-threaded CPUs, like certain high-performance computing (HPC) applications.

Source: Amazon Web Services News Introducing Optimize CPUs for Amazon EC2 Instances