The atmospheric metallicity, [M/H], and carbon-to-oxygen ratio, C/O, derived from various atmospheric retrievals of HD 209458 b. The opaque markers are the results presented in this study, whereas markers with a lower opacity are from previous literature values (e.g., Q. Xue et al. 2024; N. Bachmann et al. 2025; A. Verma et al. 2025; K. L. Chubb et al. 2026). Filled squares highlight studies that included optical data in their retrievals, which typically results in a lower retrieved [M/H] compared to analyzing infrared data alone (unfilled squares). The vertical and horizontal gray dashed lines and shaded regions represent the solar values and their respective 1σ uncertainties (M. Asplund et al. 2009, 2021). The vertical and horizontal orange dotted lines and shaded regions represent the stellar values and their respective 1σ uncertainties (A. S. Polanski et al. 2022). Symmetric uncertainties should be interpreted with caution, as they may be derived from non-Gaussian posterior distributions.