Originally Posted by
B747-437B
You WILL need a visa if you are transiting Addis en route from an international to a domestic destination in Ethiopia, even if you remain at the airport. All immigration and customs formalities will be completed at the first point of entry to Ethiopia. This assumes that you are neither Kenyan, Djiboutian nor Ethiopian in which case you do not require a visa at all.
This is a good correction to my post! I am either in transit to another (international) destination, or arriving in ADD as my final destination. "First point of entry" when you are staying in Ethiopia is key.