The single character doesn't even have alternate pronunciations, only jiu3 is listed.
However in speech I've always heard it pronounced jiu1 (example: https://youtu.be/RJFsJi7JvFI?t=10). In this other video though (https://www.youtube.com/watch?v=9lJhs4vz4eI) it's pronounced as the dictionary suggests.
Is jiu1 a pronunciation of southern dialects? How did it come about?