Yesterday I posted a patent showing the optical formulas for both an RF 15-35mm f/4L and an RF 16-35mm f/4L. I noted that an RF 14-35mm f/4L is rumored to be coming in 2021, and I did wonder aloud if that was a type, but it appears Canon is definitely working on an RF 14-35mm f/4L optical formula.
It looks like this design of an RF 14-35mm f/4L has an internal zoom and will likely have IS as well.
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While this patent pertains to underwater housings for the optical formulas in the patent, the formula for this lens is quite detailed. Canon News discovered this patent that also shows some rather large RF prime lenses, which you can read about at Canon News.
Note: The image for this post is the Canon RF 15-35mm f/2.8L IS USM