H I mass as a function of halo mass over a wide mass range. The integrated H I mass within R < 2R₂₀₀ (red squares) and 2R₂₀₀ < R < 5R₂₀₀ (blue solid circles) for individual clusters is shown. The M_HI–M_halo relations for group galaxies from A. Obuljen et al. (2019) and H. Guo et al. (2017) are shown as black open circles and open squares, respectively. The H I-selected dwarf galaxies (M_HI < 10⁸ M_⊙) are shown as open triangles (C. Cheng et al. 2025a). We further compare our measurements with the TNG-Cluster simulation results (green diamonds; D. Nelson et al. 2024) and the TNG100 simulation results for central galaxies (cyan shaded region) and satellite galaxies (violet shaded region; F. Villaescusa-Navarro et al. 2018). Overall, the simulation results are broadly consistent with the observations, but are systematically lower than the observed H I masses over a wide range of halo masses.