I'm not sure. I think both Sharpen AI and DeNoise AI give better results than Photo AI, plus the two separate programs can be set up in more detail. Unfortunately Topaz doesn't develop them further on the grounds that Photo AI can do the same thing. Still, I paid for the Photo AI upgrade for another year, with updates coming out every now and then, but I still mostly use both Sharpen AI and DeNoise AI - but increasingly I reduce noise directly in Camera Raw.