Will AWS S3 reject a read during an object being updated

Question

According to the S3 documentation, a PUT is always an atomic write to an object. My unsophisticated intuition says that the atomicity might be guaranteed by some sort of hidden locking mechanism. Does that imply that reads for objects with the same key will be ignored while an object is being updated? (I looked through the S3 documentation but couldn't find a satisfactory response.)