S3 Bucket Default Storage Class

Unfortunately the current behavior of S3 is that everything that every object put on S3 that has no explicit storage class set will be stored with S3 Standard Storage class: https://docs.aws.amazon.com/AmazonS3/latest/userguide/storage-class-intro.html#sc-howtoset

I recommend that you reach out to your AWS Account Representative to address these need. They will make sure that your use case will be added to our list of customer demands which will influence our planning for future development and prioritization.

There's no way to set a "default" storage class, but to add on to @Adreas_S's comment, you can specify the storage class when creating/uploading a new object. For example, when creating objects using the PUT Object, POST Object, and Initiate Multipart Upload APIs, you add the x-amz-storage-class request header to specify a storage class. If you don't add this header, Amazon S3 uses Standard, the default storage class.

Same holds true if you happen to be uploading objects via the AWS Command line you can use the --storage-class INTELLIGENT_TIERING parameter. For example:

aws s3 cp <source file> s3://<destinationBucket> --storage-class INTELLIGENT_TIERING

This is all outlined in Andrea's link above.