I have cited a recent pre-print posted in arxiv in one of my papers that is accepted for presenting in a conference. One of the reviewers (who is one of the authors of the pre-print I suspect) has suggested the cite the pre-print as an accepted version in an upcoming conference (different from where my paper is accepted). Now, the suggested conference does not have its proceedings published yet. The only evidence that this pre-print will be included in the final proceedings is the fact that it is mentioned in the published technical program.
Is it appropriate to cite the paper as published or should I keep the citation as a pre-print?