Student or Learner
Is it acceptable to use the perfect infinitive after "to be going to". I always thought that it's not but I have come across this sentence.
It’s going to have been 10 years since it first aired in September and quite a few members of the cast and crew will already be there.
Is it OK to say so? Or would it better just to use "It's going to be 10 years"?
It's grammatical. The only reason not to say it that way is that there are simpler constructions, such as the one you've given, and "It will have been 10 years ..."