So says ESPN:

Shayne Gostisbehere, 25, D $4.5 million through 2022-23

Ron Hextall has done a lot of good work lately, but inking Gostisbehere to this contract last summer might have been one of the GM’s finest moves. The 25-year-old defenseman is a building block of the next Flyers core (many of those players are still developing in the minors). With 150 points in his first three seasons, it feels like Gostisbehere is still realizing his potential; and even if this is as good as he gets, the cheap cap hit will age well:

http://www.espn.com/nhl/story/_/id/24055945/nhl-best-contracts-all-31-teams-heading-2018-19-season#phi