An integrated circuit system, comprising: a package substrate having a programmable integrated circuit, IC, die and a companion IC die mounted thereon, the programmable IC die including a programmable fabric having first application circuitry and the companion IC die including second application circuitry; a system-in-package, SiP, bridge including a first SiP IO circuit disposed in the programmable IC die, a second SiP IO circuit disposed in the companion IC die, and conductive interconnect on the package substrate electrically coupling the first SiP IO circuit and the second SiP IO circuit; first aggregation and first dispersal circuits (110, 112) in the programmable IC die coupled between the programmable fabric and the first SiP IO circuit, where the first aggregation circuits selectively couple outputs of the first application circuitry in the programmable fabric to internal inputs of the first SiP IO circuit and the first dispersal circuits selectively couple internal outputs of the first SiP IO circuit to inputs of the first application circuitry in the programmable fabric; and second aggregation and second dispersal circuits (126, 128) in the companion IC die coupled between the second application circuitry and the second SiP IO circuit, where the second aggregation circuits selectively couple outputs of the second application circuitry to internal inputs of the second SiP IO circuit and the second dispersal circuits couple internal outputs of the second SiP IO circuit to inputs of the second application circuitry; wherein the first and second SiP IO circuits (140A, 142) are configured to multiplex multi-channel output of the first and second aggregation circuits (110, 126), respectively, onto a first plurality of physical channels implemented over the conductive interconnect; and de-multiplex input from a second plurality of channels implemented over the conductive interconnect onto multi-channel input of the first and second dispersal circuits (112, 128), respectively. a package substrate having a programmable integrated circuit, IC, die and a companion IC die mounted thereon, the programmable IC die including a programmable fabric having first application circuitry and the companion IC die including second application circuitry; a system-in-package, SiP, bridge including a first SiP IO circuit disposed in the programmable IC die, a second SiP IO circuit disposed in the companion IC die, and conductive interconnect on the package substrate electrically coupling the first SiP IO circuit and the second SiP IO circuit; first aggregation and first dispersal circuits (110, 112) in the programmable IC die coupled between the programmable fabric and the first SiP IO circuit, where the first aggregation circuits selectively couple outputs of the first application circuitry in the programmable fabric to internal inputs of the first SiP IO circuit and the first dispersal circuits selectively couple internal outputs of the first SiP IO circuit to inputs of the first application circuitry in the programmable fabric; and second aggregation and second dispersal circuits (126, 128) in the companion IC die coupled between the second application circuitry and the second SiP IO circuit, where the second aggregation circuits selectively couple outputs of the second application circuitry to internal inputs of the second SiP IO circuit and the second dispersal circuits couple internal outputs of the second SiP IO circuit to inputs of the second application circuitry; wherein the first and second SiP IO circuits (140A, 142) are configured to multiplex multi-channel output of the first and second aggregation circuits (110, 126), respectively, onto a first plurality of physical channels implemented over the conductive interconnect; and de-multiplex input from a second plurality of channels implemented over the conductive interconnect onto multi-channel input of the first and second dispersal circuits (112, 128), respectively.