Update: the prices for the lenses leaked. The RF 400mm f/2.8L IS is $11,999, and…
No surprise that after the leaks of the last days more telephoto lenses for the RF mount are rumored. Nothing to expect for this year, though.
Canon might be set to release an RF 300mm f/2.8L IS and an RF 500mm f/4L IS lens in 2021. Canon is migrating more and more of their EF lenses to the RF mount.
The RF 300mm f/2.8L IS and an RF 500mm f/4L IS are said to be much lighter and also shorter than their EF mount counterparts. A 300mm f/2.8L IS zoom might also be in the works.
Source: Canon Rumors