There is a significant qualitative difference, very obvouse one too.

The complexity of tasks GPT-6 can do are not compareable to GPT-4. We see this daily. From CVEs which became a real problem after GPT-4, generic tool use (blender, paint, etc.), agentic work (GPT-4 was at a minute or so, GPT-6 can do hours).

They broke through significant barriers in a short period of time. I would def count the agentic quality of doing hours of work as one of the main proofs.