The article addresses cultural horizons 6–2Б at Kovrizhka IV on the Vitim River, dating to ~19–18.5 ka BP. The best studied are cultural horizons 6, 3Б, 3/2, 2Г, and 2Б. The largest assemblage (~55 thousand pieces) comes from horizon 3Б, and the smallest (~1.4 thousand pieces) from horizon 2Г. In generalized technological and typological terms, techniques include pressure detachment of microblades, production of blades up to 12 cm long, coarse prismatic blades up to 5 cm long, and flakes, and facial processing of bifaces and unifaces. The technology of Kovrizhka microcore production is described. The Yubetsu technique was practiced in a minority of cases. Assemblages include scraper-like unifaces with bifacial trimming of narrow ends, bifacial tools, end-scrapers, chisel-like tools, burins, blades, and flakes with irregular marginal retouch or without retouch, used as knives, planes, burins for carving bone and horn, and end-scrapers. Differences between assemblages are caused by seasonality, duration of stay, and subsistence strategies. The general appearance of the industry indicates the early stage of the Late Upper Paleolithic of Eastern Siberia. The industry mostly correlates with the Studenoye culture of Trans-Baikal and Dyuktai culture of Yakutia. Comparison with the earlier site of Mamakan VI reveals no continuity and differences in the microcore production technique. The later industry of Bolshoy Yakor I does reveal continuity in the Yubetsu technique, but new types of burins and bifaces appear.