Kostner has represented the
Italian national team in several tournaments. His first
International Ice Hockey Federation (IIHF)-sanctioned event was the
2007 World U18 Championships Division I. Italy placed fourth in the Group A tournament while Kostner recorded one assist in five games. He returned the following year to the
2008 Division I tournament; playing in Group A Italy finished fourth again and Kostner, serving as
captain, had 7 points in 5 games. He would play in three
World Junior Championships: the
2008 Division II, the
2009 Division I, and the
2010 Division I tournaments. ==Personal life==