AWS Step Functions now supports dynamic parallelism, so you can optimize the performance and efficiency of application workflows such as data processing and task automation. By running identical tasks in parallel, you can achieve consistent execution durations and improve utilization of resources to save on operating costs. Step Functions automatically scales all resources in response to your input. 

from Recent Announcements https://aws.amazon.com/about-aws/whats-new/2019/09/aws-step-functions-adds-support-for-dynamic-parallelism-in-workflows/