[en] We report observations of CO(J = 2 → 1) and $\mathrm{C}\mathrm{O}(J=3\to <!--\; ???\; -->2)$ line emission toward the quadruply-lensed quasar RXS J1131−1231 at z = 0.654 obtained using the Plateau de Bure Interferometer (PdBI) and the Combined Array for Research in Millimeter-wave Astronomy (CARMA). Our lens modeling shows that the asymmetry in the double-horned CO(J = 2 → 1) line profile is mainly a result of differential lensing, where the magnification factor varies from ∼3 to ∼9 across different kinematic components. The intrinsically symmetric line profile and a smooth source-plane velocity gradient suggest that the host galaxy is an extended rotating disk, with a CO size of $R_{\mathrm{C}\mathrm{O}}\sim <!--\; ???\; -->6$ kpc and a dynamical mass of $M_{\mathrm{d}\mathrm{y}\mathrm{n}}\sim <!--\; ???\; -->8\times <!--\; ??\; -->{10}^{10}$ M _⊙. We also find a secondary CO-emitting source near RXS J1131−1231, the location of which is consistent with the optically-faint companion reported in previous studies. The lensing-corrected molecular gas masses are M _gas = (1.4 ± 0.3) × 10¹⁰ M _⊙ and (2.0 ± 0.1) × 10⁹ M _⊙ for RXS J1131−1231 and the companion, respectively. We find a lensing-corrected stellar mass of M _* = (3 ± 1) × 10¹⁰ M _⊙ and a star formation rate of SFR_FIR = (120 ± 63) M _⊙ yr⁻¹, corresponding to a specific SFR and star formation efficiency comparable to z ∼ 1 disk galaxies not hosting quasars. The implied gas mass fraction of ∼18 ± 4% is consistent with the previously observed cosmic decline since z ∼ 2. We thus find no evidence for quenching of star formation in RXS J1131−1231. This agrees with our finding of an elevated $M_{\mathrm{B}\mathrm{H}}/M_{\mathrm{b}\mathrm{u}\mathrm{l}\mathrm{g}\mathrm{e}}$ ratio of >0.27${}_{-<!--\; ???\; -->0.08}^{+0.11}$% compared to the local value, suggesting that the bulk of its black hole mass is largely in place while its stellar bulge is still assembling.