Currently there are 21 native Standard Prime lenses for Sony A9 and 17 of these lenses are autofocus (AF) type.
A9 also has a sensor based image stabilization system which means that all of these lenses will be stabilized when used on A9.
Since Sony A9 has environmental sealings (Weather Sealing), you may like to couple your camera with one of these 13 Standard Prime lenses with Weather Sealings.