Between 2019 and 2024, we used the Gemini-N and JWST observatories to conduct a detailed case study of the active Centaur 450P/LONEOS, whose orbit was significantly altered by a close Saturn encounter in 1992. Gemini-N Gemini Multi-Object Spectrograph optical images likely captured the first views of 450P's inactive nucleus, indicating a relatively small radius of RN = 1.8 ± 0.5 km and a surface color of g'−i' = 1.15 ± 0.09. This places 450P on the red end of the neutral/gray Centaur population and may indicate comparatively limited solar-driven surface processing relative to other known active Centaurs. A coma developed as 450P changed its heliocentric distance, RH, from 7.83 to 7.24 au, with an estimated low dust production rate of ∼4─8 kg s−1. JWST NIRSpec integral field unit prism-mode spectra revealed an elongated dust morphology and a symmetric CO2 gas distribution in the coma but no H2O or CO emission features, with production rates of QCO2 = (6.99 ± 0.07) × 1024 molecules s−1, QH2O≤ 1.2 × 1024 molecules s−1, and QCO ≤ 5.2 × 1024 molecules s−1. Absorption features at 2.0 and 3.0 μm indicate the presence of water ice and a subtle 3.1 μm feature, which is consistent with crystalline water ice in larger grains. A Hapke-style model dominated by large (Deff = 5.9 μm) dust grains with a volumetric ice fraction of fice = 33% fits the spectrum. A thermal model incorporating 450P's orbital history since ∼1500 CE aligns with the observed onset of activity driven by CO2 outgassing from amorphous water ice crystallization between 140 and 160 K.