One summary of the great Kant's view, to the extent that it can be summed up, is that he takes determinism to be a kind of fact, and indeterminism to be another kind of fact, and our freedom to be a fact too -- but takes this situation to have nothing to do with the kind of compatibility of determinism and freedom proclaimed by such Compatibilists as Hobbes and Hume. Thus Kant does not make freedom consistent with determinism by taking up a definition of freedom as voluntariness -- at bottom, being able to do what you want. This he dismisses as a wretched subterfuge, quibbling about words. Rather, the freedom he seeks to make consistent with determinism does indeed seem to be the freedom of the Incompatibilists -- origination. Is he then an Incompatibilist? Well, against that, it can be said he does not allow the existence of origination in what can be called the world we know, as Incompatibilists certainly do.
Kant's main idea, whatever sense can finally be made of it, depends on his fundamental two-worlds doctrine. He locates determinism in the empirical world or world of appearances, and freedom in the world of things-in-themselves, the world of reason. It is important that the latter world is not in time.
So he is a determinist of a kind, opposed to the tradition of Compatibilism, not really in the Incompatibilist tradition, but tries to make his determinism and freedom-as-origination consistent by his own private means. You may well wonder if he can succeed in all this -- and suspect too, at the beginning of the 21st Century, that something so radical as his view is actually needed.