Sigma is rumored to announce several super telephoto prime lenses. Recent rumors show that Sigma is working on big prime lenses. As a result Sigma 300mm and 400mm f/2.8 OS, 500mm and 600mm f/4 OS prime lenses expected to be coming in the 2014.
Canon and Nikon also produce high quality big prime lenses. But the rumor mill says that the price of the big prime lenses will be cheaper than Canon and Nikon version.
Sigma 300mm & 400mm f/2.8 OS and 500mm & 600mm f/4 OS Prime Lenses Coming in 2014The Sigma 200-500mm f/2.8
Official announcement of Sigma 300mm and 400mm f/2.8 OS, 500mm and 600mm f/4 OS prime lenses expected to be in 2014.