If Tesla can really do everything they said they will do on battery day then the 4680 will be far cheaper per kWh than Ultium. But that remains to be seen.The 4680s are definitely cheaper to produce on a per-unit basis, but not necessarily on a per-kWh basis. Also, cylindrical cells cost a lot more to integrate into a pack than pouch or prismatic cells, which offsets a lot of the savings from making the cylindrical cells in the first place. It's important to remember that much of Tesla's battery cost advantage was based on chemistry (lower cobalt use), and the first generation Ultium cells are using a similar amount of cobalt as Tesla's current chemistry.
All we know at this point is that Tesla is targeting sub $100 per kWh cell costs while GM is claiming sub $100 per kWh finished pack costs for their first generation Ultium packs.