According to CR, New Canon super telephoto lenses, specifically the RF 400mm and RF 600mm, are rumored to be announced in May
Even if Canon does issue a development announcement for these “big white lenses,” I believe it is unlikely that we will get wind of the information prior to the official announcement itself. Any leaks would likely surface only a day or two beforehand. B&H Photo currently lists a projected arrival date of April 13, 2026, for new products; however, such dates rarely turn out to be accurate.
Given that Canon’s RF400mm F2.8L and RF600mm F4L lenses inherited their optical systems from their EF-mount predecessors—meaning their optical designs are now quite dated—it would come as no surprise to see them undergo a model refresh at this stage. It will be fascinating to see whether the new models follow the recent trend in telephoto lenses by prioritizing a more compact and lightweight design, or if they instead focus on enhanced convenience through the inclusion of built-in teleconverters.