A main top of a gas cooktop appliance defining vertical, lateral, and transverse directions includes a front edge, a bottom surface, a top surface, and a transition surface. The front and rear edges are spaced apart from one another along the transverse direction. The bottom surface is positioned between the front and rear edges along the transverse direction, and the bottom defines a first plurality of openings. The top surface is spaced apart from the bottom surface along the vertical direction, and the top surface surrounds a perimeter of the bottom surface. The top surface defines a second plurality of openings positioned between the bottom surface and the front edge along the transverse direction. The transition surface extends between the bottom surface and the top surface along the vertical direction, and is spaced apart from the front edge along the transverse direction. The transition surface also defines an opening.