The Blues assigned Kostin to Avangard in September. He had 18 points (7g, 11a) with a +6 plus/minus rating and 50 penalty minutes in 43-regular season games.
With the KHL season now concluded, Kostin will be eligible to return to St. Louis and join the Blues. He would be subject to the NHL's quarantine protocols before joining the team.
Kostin was drafted by St. Louis in the first round (No. 31 overall) at the 2017 NHL Draft. He played in four regular-season games for the Blues in the 2019-20 season, posting one goal. In three seasons with the AHL's San Antonio Rampage, Kostin has posted 29 goals and 53 assists (82 points) in 181 games.