Open Theist Tom Belt claims God is the Summum Bonum:

Just thinking out loud. Chime in if you want. God, all theists would agree, is the summum bonum—the greatest good, the highest value. I’m going to assume that here. What I’d like to suggest in addition to this (though it is nothing new) is that this highest value is God’s experience, more precisely his experience of “beatitude” or “unsurpassable aesthetic satisfaction” (to employ Greg’s expression from Trinity & Process). You might be thinking that I’ve said this all before and wonder what’s new here? Just this: God’s experience of his own beatitude is that about God which constitutes God as the summum bonum and that from which all created experiences derive their value.