We show that the rheology of a silazane-based precursor for a silicon carbonitride ceramic can be radically altered by reacting it with an alkoxide precursor. This modified precursor can be drawn into fibers by a simple process. The fiber-friendly rheology of the modified precursor is ascribed to the creation of linear polymer chains by a reaction between silazanes and alkoxides. The ceramic fibers made by this process have excellent mechanical properties, reaching tensile strengths of 2.8 GPa. Their structure is amorphous.