This article reports a synthesis that yields 4.4 g of Cu nanowires in 1 h, and a method to coat 22 g of Cu nanowires with Ag within 1 h. Due to the large diameters of Cu nanowires (≈240 nm) produced by this synthesis, a Ag:Cu mol ratio of 0.04 is sufficient to coat the nanowires with ≈3 nm of Ag, and thereby protect them from oxidation. This multigram Cu‐Ag core–shell nanowire production process enabled the production of the first nanowire‐based conductive polymer composite filament for 3D printing. The 3D printing filament has a resistivity of 0.002 Ω cm, >100 times more conductive than commercially available graphene‐based 3D printing filaments. The conductivity of composites containing 5 vol% of 50‐µm‐long Cu‐Ag nanowires is greater than composites containing 22 vol% of 20‐µm‐long Ag nanowires or 10‐µm‐long flakes, indicating that high‐aspect ratio Cu‐Ag nanowires enable the production of highly conductive composites at relatively low volume fractions. The highly conductive filament can support current densities between 2.5 and 4.5 × 105 A m−2 depending on the surface‐to‐volume ratio of the printed trace, and was used to 3D print a conductive coil for wireless power transfer.