In 2004, Athearn was purchased by Horizon Hobby, and with the purchase many new features and projects were added to the Athearn Genesis line. Two new models, the MP15AC and SD45-2, were introduced to the brand in 2005 and later in 2009 Athearn established a relationship with SoundTraxx and begin offering locomotives with Tsunami sound. A new decade would bring more famous models such as: the Genesis SD70M-2, GP7 & GP9; DDA40X "Centennial"; GP15T; Southern Pacific Bay Window Caboose; 50' GATC 20,000 Gallon SHN Type 40 Acid Tank Car; and 50' PC&F Box Car with 8'+8' Landis Doors.

Throughout the next decade, the Athearn Genesis line would become the definition of the highest fidelity in prototype accuracy in the industry. Locomotives with not only road name specific details, but road number details, an industry first, became available to the model railroader. Modelers could now spend more time working on their layout than building a fleet of prototype accurate locomotives and rolling stock. Seeing a trend of both individual and cottage industry “weathering” of models, Athearn Genesis also unveiled another industry first,: Primed for Grime. Primed for Grime would allow the modeler to accurately run a locomotive that was no longer factory fresh but featured the faded and patched paint of a veteran unit. In 2022, Athearn added Athearn Genesis N to its growing product line. Like the HO counterparts, these N scale model trains would include separately applied detail parts, cut levers and air hoses, and road number specific details and paint schemes, something not seen in the N scale world before. For the most accurate in HO and N scale models, no other brand can match Athearn Genesis.