Nikon is developing a 400MM F/2.8 TC VR S Super-Telephoto Prime Lens with a built-in 1.4x teleconverter.
The NIKKOR Z 400mm f/2.8 TC VR S, the first NIKKOR Z super-telephoto prime lens, is part of the S-Line of NIKKOR Z lenses. Nikon claims that the NIKKOR Z 400mm f/2.8 TC VR S is able to achieve beautiful bokeh and high resolution. It will feature a built-in 1.4x teleconverter and a new coating that delivers the highest anti-reflection performance in NIKKOR history. Nikon states that the operability and the way it has been designed will make it ideal for video recording.
If you are hoping this comes out soon, you are out of luck. This lens won’t be available till 2023.