HD 18438 is a cool M-dwarf (about 1.84 solar masses, 3,860 K, 88.5 solar radii), 224 light-years from Earth. HD 18438 b is a 21.0-Jupiter-mass companion, with an orbital period of 2.20 years, at 2.100 AU from its star, on an eccentric orbit (e ≈ 0.10), discovered in 2023 via radial velocity. The planet betrayed itself through the star's reflex motion — a technique that first revealed worlds around Sun-like stars in the 1990s and remains a workhorse of exoplanet discovery. HD 18438 b circles in the outer system, comparable to the Jupiter region.