Hartshorne is among those on the list of "proto" speculative philosophers within the twentieth century who endorse contingency, realism, and variant forms of agential materialism. Others include Whitehead (of course) and Justus Buchler. See Hartshorne's "Contingency in the New Era of Metaphysics" HERE
I found it interesting, and true, when Alex Galloway said that Laruelle, for example, was the first "anti-correlationist."
Sometimes looking back a step can help us move a few steps forward.