According to public information, AWS uses both and not only. AWS wrote a paper on the topic with some details about their applications of formal methods^1. AWS

According to public information, AWS uses both and not only. AWS wrote a paper on the topic with some details about their applications of formal methods^1. AWS is a large org though, it would be hard to generalise or reduce their approach to any single method. 1: https://www.amazon.science/publications/using-lightweight-formal-methods-to-validate-a-key-value-storage-node-in-amazon-s3 https://www.amazon.science/publications/using-lightweight-fo... Later add: I believe P creator is employed by AWS at this moment.