As already confirmed several days ago, Canon will announce two big white super telephoto prime lenses before Photokina 2018. Now we just receive more info about the these lens announcement date.
Based on several of our sources, the EF 400mm f/2.8L IS III USM lens and EF 600mm f/4L IS III USM lens will be officially announced on September 4th to September 5th next week.
As CR also said, we are unlikely to see camera announcements (EOS M5 Mark II, Full Frame Mirrorless Cameras, EOS 7D Mark III, EOS 90D) before Photokina. Though there is still a chance that we will see development announcement for Canon full frame mirrorless cameras before Photokina. Stay tuned.