The JWST transmission spectroscopy of TOI-199b, a Saturn-sized world at ~175°F orbiting every 100 days, marks the initial high-resolution atmospheric probe of any temperate giant exoplanet. Researchers from Penn State and JPL collected 20 hours of baseline stellar spectra plus a 7-hour transit window, detecting methane absorption features that distinguish this object from both solar-system ice giants and hot Jupiters. Unlike the 1992-era radial-velocity detections that merely confirmed existence, this peer-reviewed Astronomical Journal study (May 2026) enables direct comparison of carbon chemistry across temperature regimes. The work exposes a gap in formation models that under-predict methane retention at intermediate insolations; extending these data to the handful of other known temperate giants could test whether core-accretion plus migration pathways produce consistent envelope compositions. Limitations remain stark: a single-planet sample precludes statistical inference, and the gas-giant radius precludes direct habitability analogies despite the Earth-like temperature. Still, the measurement pipeline validates JWST's capacity for longer-duration transits, accelerating the move from discovery to compositional taxonomy that ultimately informs terrestrial-atmosphere retrievals.