Mis-led. It goes faster than light can go in the same medium, resulting in an 'optical sonic boom'. But, light goes less than c through air, and even more slowly through water (hence, refraction!).... In fact, near 0 K, in an Einstein Condensate (Google it), the speed of light is nearly zero, b/c of the density of the material.
At the moment, I think that nothing can go faster than c, the speed of light in a vacuum. Tachyons are theoretical. However, I haven't read the recent research on neutrinos going faster than c !!! That is a game changer..... No reason why Einstein was right, any more than Newton