Siblings Autism

Me and my partner are having a baby in a few months and he has just asked what might be the chances of our baby being autistic as his son is. All I can find is studies for full siblings and not for half. His son is diagnosed but my partners father self diagnosed himself with it which Im not sure how accurate the online test would be but apart from that we know of no one else with it. So what would be the chances?

I don’t mind if our baby is or not but just curious