A counter-flow heat exchanger including a core region and a plenum region. The core region including a first set of heat exchanging passageways and a second set of heat exchanging passageways disposed at least partially therein. A plenum region is disposed adjacent opposed distal ends of the core region. Each of the plenum regions including a fluid inlet plenum, a fluid outlet plenum and a tube plate disposed therebetween. The first set of heat exchanging passageways is truncated and defines a first tube-side fluid flow path in a first direction. The second set of heat exchanging passageways defines a second tube-side fluid flow path in a second opposing direction. Each of the heat exchanging passageways extending from a fluid inlet plenum to a fluid outlet plenum. The tube plates and the core region include one of a cast metal formed thereabout each of the heat exchanging passageways or a braze bond formed between each of the heat exchanging passageways.