A heat exchanger comprising: a core that receives a plurality of mediums (4 01, 402); a first manifold (110, 410) comprising a plurality of first independent sub-units (410-1, 410-2, 410-3) receiving a specified portion of a flow of a first medium of the plurality of mediums, each first independent sub-unit comprising a first end receiving the specified portion of the first medium, a second end intersecting the core at a first manifold/core interface, and a plurality of first individual layers being cantilevered and flexible, the plurality of first individual layers providing gradual transitions for the specified portion of the first medium from the first end to the second end to reduce or eliminate discontinuities at the first manifold/core interface that cause stress to the heat exchanger; and a second manifold (314, 414) comprising a first end intersecting the core at a second manifold/core interface and receiving the specified portion of the flow of the first medium of the plurality of mediums from the core, the second manifold comprising a plurality of second independent sub-units, each second independent sub-unit comprising a plurality of second individual layers providing gradual transitions for the first medium from the first end of the second manifold to a second end of the second manifold to reduce or eliminate discontinuities at the second manifold/core interface that cause stress to the heat exchanger, wherein the gradual transitions are constructed via additive manufacturing to provide continuous, homogeneous transitions across the first and second manifold/core interface for the first medium. a core that receives a plurality of mediums (4 01, 402); a first manifold (110, 410) comprising a plurality of first independent sub-units (410-1, 410-2, 410-3) receiving a specified portion of a flow of a first medium of the plurality of mediums, each first independent sub-unit comprising a first end receiving the specified portion of the first medium, a second end intersecting the core at a first manifold/core interface, and a plurality of first individual layers being cantilevered and flexible, the plurality of first individual layers providing gradual transitions for the specified portion of the first medium from the first end to the second end to reduce or eliminate discontinuities at the first manifold/core interface that cause stress to the heat exchanger; and a second manifold (314, 414) comprising a first end intersecting the core at a second manifold/core interface and receiving the specified portion of the flow of the first medium of the plurality of mediums from the core, the second manifold comprising a plurality of second independent sub-units, each second independent sub-unit comprising a plurality of second individual layers providing gradual transitions for the first medium from the first end of the second manifold to a second end of the second manifold to reduce or eliminate discontinuities at the second manifold/core interface that cause stress to the heat exchanger, wherein the gradual transitions are constructed via additive manufacturing to provide continuous, homogeneous transitions across the first and second manifold/core interface for the first medium.