The Nikon Nikkor Z 800mm f/6.3 VR PF S lens is rumored to be announced this week:
I still do not have the exact date, but I believe it will most likely be on April 6th (it could be earlier):
Nikon Nikkor Z 800mm f/6.3 VR PF S lens updates (price: $6k, weight: 2.3 kg!)
The Nikon NIKKOR Z 800mm f/6.3 VR S lens is coming soon – already listed at B&H
Nikon Nikkor Z 800mm f/6.3 VR S lens development announcement