We run on the same instance types the larger PlanetScale Metal sizes offer as whole instances. For Intel that's r6id, i4i, i7i, i3en, and i7ie. For ARM that's r8gd, i8g, and i8ge. (Right now, at least. AWS is always cookin' up new instance types.) Same story will soon be true for GCP.
Would be curious to know what the underlying aws ec2 instance is.
Is each DB on a dedicated instance?
If not, are there per-customer iops bounds?