Supplementary Figures and Model Grid Files for: The SPHINX M dwarf Spectral Grid II. New Model Atmospheres and Spectra to Derive Fundamental Properties of mid-to-late type M dwarfs

This record contains the supplementary materials associated with Iyer et al. 2025 and the SPHINX II M-dwarf atmosphere model grid files. Description of Supplementary Figures included: • Fully converged posterior corner plots for each grid-model retrieval fit presented in the paper• Corresponding best-fit synthetic spectra compared against SpeX/IRTF observations used in the analysis These materials provide full visualization of the statistical constraints on stellar properties inferred using SPHINX II. Please refer to the published manuscript for target selection, modeling methodology, and interpretation. Model directory information: Install via homebrew: brew install p7zip Example extraction (bash): 7z x SPHINXII_condcloud.7z -oSPHINXIIMODELS/ All SPHINX II model "flavors" include:• ATMS/ — atmospheric structure profiles• SPECTRA/ — disk-integrated stellar spectra Model sets included in this record: 1) SPHINXII_condcloud — physical condensate clouds with sedimentation balance (Ackerman & Marley 2001) and cloud–convection feedback (Lefèvre et al. 2022). 2) SPHINXII_graycloud — vertically uniform gray cloud opacity; mixing-length parameter αMLT = 1.0. 3) SPHINXII_graycloud_MLT0.5 — same as (2) but with αMLT = 0.5. Includes the fixed minimal gray-opacity grid (log κ = –29) used in Figure 5 of the paper. A development mirror of these model grids (and an issue tracker) is maintained on GitHub for convenience.The official, citable, archived dataset is this Zenodo record, which should be cited together with the ApJ publication. For SPHINX I (cloud-free) model grids, please refer to the separate Zenodo DOI archived as part of SPHINX Paper I.