A rotor for a gas turbine engine comprising: a first rotor disk defined along an axis of rotation and a second rotor disk spaced axially aft of the first rotor disk; a first plurality of blades which extend from the first rotor disk and a second plurality of blades which extend from the second rotor disk; at least a first spacer (62CA; 62CA') positioned upstream of the first plurality of blades and a second spacer positioned between the first and second pluralities of blades, wherein the spacers (62C, 62CA, 62CA') each include a spacer outer peripheral surface; wherein each rotor disk includes a rotor outer peripheral surface, and wherein the first and second pluralities of blades are each supported on respective platforms that have a platform inner surface that faces the rotor outer peripheral surface, characterised in that: the second spacer includes a plurality of core gas path seals that are each separated from a rotor ring at an interface defined along a spoke, and wherein the second spacer includes a spacer inner surface that faces the axis of rotation, and wherein a flow passage is defined between the rotor outer peripheral surface and the platform inner surface, and between the spacer inner surface and a rotor ring outer surface such that the flow passage extends from the first rotor disk through the second spacer and into the second rotor disk; and a plurality of inlets (88; 88') formed within at least one of the spacer outer peripheral surface and a spacer inner surface of the first spacer (62CA; 62CA') to pump air into the flow passage. a first rotor disk defined along an axis of rotation and a second rotor disk spaced axially aft of the first rotor disk; a first plurality of blades which extend from the first rotor disk and a second plurality of blades which extend from the second rotor disk; at least a first spacer (62CA; 62CA') positioned upstream of the first plurality of blades and a second spacer positioned between the first and second pluralities of blades, wherein the spacers (62C, 62CA, 62CA') each include a spacer outer peripheral surface; wherein each rotor disk includes a rotor outer peripheral surface, and wherein the first and second pluralities of blades are each supported on respective platforms that have a platform inner surface that faces the rotor outer peripheral surface, characterised in that: the second spacer includes a plurality of core gas path seals that are each separated from a rotor ring at an interface defined along a spoke, and wherein the second spacer includes a spacer inner surface that faces the axis of rotation, and wherein a flow passage is defined between the rotor outer peripheral surface and the platform inner surface, and between the spacer inner surface and a rotor ring outer surface such that the flow passage extends from the first rotor disk through the second spacer and into the second rotor disk; and a plurality of inlets (88; 88') formed within at least one of the spacer outer peripheral surface and a spacer inner surface of the first spacer (62CA; 62CA') to pump air into the flow passage. the second spacer includes a plurality of core gas path seals that are each separated from a rotor ring at an interface defined along a spoke, and wherein the second spacer includes a spacer inner surface that faces the axis of rotation, and wherein a flow passage is defined between the rotor outer peripheral surface and the platform inner surface, and between the spacer inner surface and a rotor ring outer surface such that the flow passage extends from the first rotor disk through the second spacer and into the second rotor disk; and a plurality of inlets (88; 88') formed within at least one of the spacer outer peripheral surface and a spacer inner surface of the first spacer (62CA; 62CA') to pump air into the flow passage.