As you know I don’t post all rumors I get. I try to sum up the less reliable in my “wild rumors” roundup post. I checked a rumor I got two months ago from a new source and I think that in this case the new source might actually be spot on! He told me this many weeks before the official Sony 300mm GM development announcement:
There might be 300mm f/2.8 GM and 800mm f/5.6 GM in 2023
As you obviously see he was right on the 300mm GM. So maybe Sony will announce a new 800mm f/5.6 lens sometimes in 2023 that will then be available in 2024?