Self-consistent modeling of the atmosphere of KELT-1b. Top: model day-side spectra (left) and pressure-temperature (P-T) profiles (right), assuming solar metallicity and an internal temperature of 1500 K. The red spectrum and P-T profile correspond to a C/O=0.5 and depleted TiO/VO (e.g., due to gravitational settling), while the blue model corresponds to a C/O = 1. The black dashed lines correspond to blackbody spectra at 3000 and 3200 K. The cloudy, T_int = 1000 K model from Beatty et al. (2020) is shown in grey for reference. Bottom: model night-side spectra (left) and pressure-temperature profiles (right) for KELT-1 b assuming internal temperatures of 1500 K (red lines) and 2000 K (purple lines). Dashed black lines correspond to blackbody spectra at 750, 1000 and 1500 K. Flux is shown in SI units (W sr⁻¹ m⁻³). In both panels, data are shown by black points and error bars. Coloured circles show the binned model spectra. Vertical gray bands show the TESS and Spitzer bandpasses.