Gilbert, a second-round pick in the 2011 draft, has started 34 games in three seasons. He was selected as the team's outstanding rookie after making 13 starts at left tackle in 2011. He missed the last 11 games of the 2012 season with an ankle injury and switched to right tackle last season.
The 26-year-old Gilbert is the second lineman the Steelers have locked up to a long-term deal in recent months. Pittsburgh signed three-time Pro Bowl center Maurkice Pouncey to a six-year extension in June.
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