I dont believe aws have ever said.

My long held suspicion is they designed the product slos/apis to allow for the underlying storage technology to change without customers being aware, hence its clearly inspired by tape access patterns.

Possibly some of the very largest aws regions use tape libraries.

But I suspect aws co-mingles the data with S3 and just wears the cost. They've been known to price below cost (eg lambda implementation before firecracker) to corner the market.