Kammala jumla mai zuwa: Ta hanyar buga wasanni da yawa, an dauki Kostin tare da zabin karshe a zagaye na farko na
2017 NHL Entry Draft da St. Louis Blues suka yi. Da farko an yi tunanin ci gaba da haɓaka a Rasha, an sanya Kostin a matsayin ɗan wasa kyauta bayan Dynamo Moscow an tilasta masa sakin duk 'yan wasan su ta hanyar keta dokokin KHL a ranar 4 ga Yuli 2017. Kashegari, Kostin ya amince da kwangilar shiga shekaru uku tare da St. Louis Blues. Kostin ya ce zai fi son yin wasa a cikin NHL don kakar 2017-18, kodayake ba zai yi adawa da zuwa gasar Hockey ta Amurka ba (AHL), babbar ƙungiyar ƙwararrun ƙwararrun NHL; duk da haka ba shi da sha'awar yin wasa a WHL, ko kowane rukuni na matasa.