I am in the process of getting divorced from Thai wife. We have 5 year old son, born in Thailand, but German Citizen.

The other party is offering JOINT CUSTODY with specific visitation rights for the mother (child lives with the father). Such an agreement would be signed by a judge.

Is such Joint Custody enough to get 1 year visa extension based on raising a Thai child, or does immigration only accept Sole Custody.

Any advice from the legal department?

RJ

As said in your other thread, the child is also Thai. Otherwise you wouldn't be able to get extensions of stay.

Joint custody is all you will get from a Thai judge, unless the mother is a danger to the child or doesn't want custody over the child.

Normally it is enough that you are the prime caretaker of the child, the child has to be living with you. But it also depends on how the immigration office interprets the rule, some seem to be more strict than others and want sole custody. But the child living with you and visitation rights for the mother should be enough.