Ours started open, but mostly just pictures and letters at first. Our birth mom was really stable, mature, and pro adoption from the beginning, and has become more so over time. We now see her a couple times a year. Our son knows he is loved by so many people. Our birth dad is immature, flakey and has been in some trouble over the years. He has become a bit more stable and interested and so we have opened up and send pictures of gifts maybe once every other year now.
It is good to be both tempered and honest up front. It is really painful to birth parents to promise openness and then close up once the papers at signed. Not all birth parents are good influences or good at openness, but if you have good birth parents it can lead to beautiful and close relationships, and closure and comfort for the child.