Bhagavad Gita, Chapter 15, Verse 18

As I transcend the Perishable and am above even the Imperishable, therefore am I in the world and in the Veda celebrated as the Purushottama, the Highest Purusha.

Being beyond even the imperishable is named here as a real, specific claim, not just another way of saying great.

Krishna places himself beyond both categories just described, perishable and imperishable alike. Real transcendence here means genuinely exceeding even what already seemed like the highest classification.