Research into agricultural adoptions and dispersals of major domesticated plant taxa across the ancient Eurasian steppe has gained significant momentum in the past decade. Archaeobotanical data have clarified the antiquity and breadth of these processes, revealing the contours of agricultural developments throughout the Bronze and Iron Ages and linking them to a broader trans-Eurasian system of dynamic long-term social, economic, and biogeographic interactions. The prehistory of agriculture in the easternmost steppe– the Mongolian steppe– nevertheless remains an open question, persistently deemed an unexplained “outlier." This paper addresses our evolving knowledge of the origins and development of agriculture on the Mongolian steppe and considers a range of new interdisciplinary data as well as macroremain evidence from a newly discovered prehistoric agricultural site in northeastern Mongolia. We focus particularly on recent finds at Khairt Suuryn (c. 250 BC-200 AD), an extensive subterranean pithouse settlement representing only the third prehistoric agricultural site currently known in Mongolia. Khairt Suuryn has yielded evidence for production of broomcorn millet (Panicum miliacium) and large cereal grains (cf. Triticum aestivum), as well as the first documented recovery of foxtail millet (Setaria italica) prior to the medieval period. Rather than isolation from the changing subsistence economies surrounding it, new macrobotanical and biomolecular data across Mongolia suggest mosaic patterns of early agricultural participation that cohere temporally and spatially with better documented areas of the Eurasian steppe and Inner Asia. We posit that Mongolia's longstanding perception as an outlier to supraregional prehistoric agricultural developments reflects long-term research trends rather than prehistoric realities. Finally, we advocate strongly for standardized inclusion of archaeobotanical research design and sampling on excavations in the Mongolian steppe region in order to resolve ongoing research disparities.