According to CR3, Canon RF 200-500mm F4L IS USM lens will be officially announced in Q4 2023, or perhaps in Q1 of 2024 ahead of Canon EOS R1.
Canon RF 200-500mm F4L IS USM lens will not have a built-in teleconverter. But don’t worry, there is a nice teleconverter for both Canon RF 100-300mm F2.8 L IS USM and Canon RF 200-500mm F4L IS USM lens.
A built-in teleconverter makes the lens bigger and heavier, but Canon wants to make this type of lens as light as possible.
It is interesting to see what the specifications of this new teleconverter will be. It would be interesting if the previously patented 1.0x-1.5x-2.0x teleconverter with variable magnification is commercialized.
Read more Canon RF Lenses Roadmap 2023