We all remember the 2015 Canon EXPO, and that glorious looking prototype for the Canon EF 600mm f/4 DO IS on display. What Canon didn't tell us is when it was going to be added to the EF lens lineup.
There have been mentions that “this is the year” a few times over the last couple of years, and we have been guilty of writing that a couple of times.
We have been asking a lot over the last few months about the prospects of the EF 600mm f/4 DO IS coming in 2018, and we're sad to say, the prospects don't look good. We're told that an official announcement isn't expected this year.
There is always a possibility of a development announcement at Photokina, but I don't believe we've ever heard about a development announcement from Canon before they do the announcing.