Cooktop appliance with a gas burner assembly

A cooktop appliance, comprising:

• a top panel;
• and
• a gas burner assembly positioned at the top panel, the gas burner assembly comprising an annular burner body positioned on the top panel at a top surface of the top panel, the annular burner body defining a central combustion zone, the annular burner body also defining a plurality of flame ports at the central combustion zone, gaseous fuel flowable from a fuel chamber within the annular burner body into the central combustion zone through the plurality of flame ports, the gas burner assembly further comprising a fuel manifold, the annular burner body connectable to the fuel manifold such that the gaseous fuel is flowable from the fuel manifold into the fuel chamber of the annular burner body, the fuel manifold having a plurality of outlet passages and a horizontal Venturi mixing tube, the gaseous fuel flowable through the plurality of outlet passages into the fuel chamber of the annular burner body, the horizontal Venturi mixing tube having an inlet positioned at one side portion of the fuel manifold and an outlet positioned at an opposite side portion of the fuel manifold,
• wherein the annular burner body is open at the central combustion zone such that the top panel is exposed through the annular burner body at the central combustion zone.