Fluid injector - with a solid state actuator and - with an injector body - which has an actuator recess in which the solid state actuator is arranged, - with a control piston unit which is arranged in a control piston unit recess of the injector body, - with a transmission pin which is arranged such that it penetrates a transmission pin recess in the injector body and mechanically couples the solid state actuator to the control piston unit, - wherein a first control chamber is delimited by the control piston unit and injector body, and the first control chamber is hydraulically coupled to a second control chamber, - wherein a nozzle body is provided having a nozzle body recess in which, in a region of a nozzle tip of the nozzle body, one or more injection holes are formed penetrating the nozzle body towards the outside, - wherein a nozzle needle is arranged in the nozzle body recess and has a face facing away from the needle tip which delimits the second control chamber, - wherein the nozzle needle is arranged axially moveably in the nozzle needle recess such that in a closed position it prevents a fluid flow through the one or more injection holes and otherwise allows this, - wherein the control piston unit - has a control piston which, at an axial end facing the transmission pin, has a face which is coupled to the transmission pin and delimits the first control chamber, - has a control sleeve which is arranged coaxially to the control piston and has a radially inwardly directed protrusion, via which a carrier coupling takes place between the control piston and the control sleeve after overcoming a predefined first piston stroke of the control piston caused by an elongation of the solid state actuator which is due to the supply of electrical energy, wherein the control sleeve is arranged and configured such that during an axial movement of the control piston with the existing carrier coupling, it influences a free volume of the first control chamber. - with a solid state actuator and - with an injector body - which has an actuator recess in which the solid state actuator is arranged, - which has an actuator recess in which the solid state actuator is arranged, - with a control piston unit which is arranged in a control piston unit recess of the injector body, - with a transmission pin which is arranged such that it penetrates a transmission pin recess in the injector body and mechanically couples the solid state actuator to the control piston unit, - wherein a first control chamber is delimited by the control piston unit and injector body, and the first control chamber is hydraulically coupled to a second control chamber, - wherein a nozzle body is provided having a nozzle body recess in which, in a region of a nozzle tip of the nozzle body, one or more injection holes are formed penetrating the nozzle body towards the outside, - wherein a nozzle needle is arranged in the nozzle body recess and has a face facing away from the needle tip which delimits the second control chamber, - wherein the nozzle needle is arranged axially moveably in the nozzle needle recess such that in a closed position it prevents a fluid flow through the one or more injection holes and otherwise allows this, - wherein the control piston unit - has a control piston which, at an axial end facing the transmission pin, has a face which is coupled to the transmission pin and delimits the first control chamber, - has a control sleeve which is arranged coaxially to the control piston and has a radially inwardly directed protrusion, via which a carrier coupling takes place between the control piston and the control sleeve after overcoming a predefined first piston stroke of the control piston caused by an elongation of the solid state actuator which is due to the supply of electrical energy, wherein the control sleeve is arranged and configured such that during an axial movement of the control piston with the existing carrier coupling, it influences a free volume of the first control chamber. - has a control piston which, at an axial end facing the transmission pin, has a face which is coupled to the transmission pin and delimits the first control chamber, - has a control sleeve which is arranged coaxially to the control piston and has a radially inwardly directed protrusion, via which a carrier coupling takes place between the control piston and the control sleeve after overcoming a predefined first piston stroke of the control piston caused by an elongation of the solid state actuator which is due to the supply of electrical energy, wherein the control sleeve is arranged and configured such that during an axial movement of the control piston with the existing carrier coupling, it influences a free volume of the first control chamber.