Currently there are 12 native Telephoto Prime lenses for Pentax K-1 and 6 of these lenses are autofocus (AF) type.
K-1 also has a sensor based image stabilization system which means that all of these lenses will be stabilized when used on K-1.
Since Pentax K-1 has environmental sealings (Weather Sealing), you may like to couple your camera with one of these 1 Telephoto Prime lenses with Weather Sealings.