[ak217]

No, when copying objects between buckets (aws s3 cp s3://... s3://... and the corresponding sync command), the AWS CLI uses CopyObject (https://docs.aws.amazon.com/AmazonS3/latest/API/API_CopyObje..., previously known as S3 PUT Copy), in which the client doesn't handle any object contents. The call stack eventually reaches https://github.com/boto/s3transfer/blob/develop/s3transfer/c... (or its multipart equivalent), where it calls the botocore binding for this API.