Spin frequency evolution of RX J0520.5–6932 during the 2024 outburst. Top: Barycenter-corrected spin frequencies from NICER, AstroSat, Fermi/GBM and NuSTAR, overlaid with the composite model ν(t) = ν_int(t)−ν_orb(t) (solid red line), which combines the intrinsic quadratic spin evolution with the fixed orbital parameters from Yang et al. (2025) (Solution II). Middle: Spin frequencies after correcting for orbital motion. A quadratic model (solid line) fits all data points and captures the evolving spin-up trend, while a linear model (dashed line) fits only the early part of the outburst (excluding the final NICER point). Bottom: Residuals of the quadratic and linear fits. The residuals clearly favor the quadratic model, supporting the presence of a varying spin-up rate during the outburst.