The Kondo-lattice compound CeRhIn5 displays a field-induced Fermi surface reconstruction at B* approximate to 30 T, which occurs within the antiferromagnetic state, prior to the quantum critical point at B-c0 approximate to 50 T. Here, in order to investigate the nature of the Fermi surface change, we measured the magnetostriction, specific heat, and magnetic torque of CeRhIn5 across a wide range of magnetic fields. Our observations uncover the field-induced itineracy of the 4f electrons, where above B-onset approximate to 17 T there is a significant enhancement of the Sommerfeld coefficient, and spin-dependent effective cyclotron masses determined from quantum oscillations. Upon crossing B-onset, the temperature dependence of the specific heat also shows distinctly different behavior from that at low fields. Our results indicate that the Kondo coupling is remarkably robust upon increasing the magnetic field. This is ascribed to the delocalization of the 4f electrons at the Fermi surface reconstruction at B*.