According to Ed Bouchette:
The Steelers came to one final contract extension before the regular season starts when center Justin Hartwig today signed a four-year, $10 million contract. The deal includes a $2.1 million signing bonus.
It will be the final contract extension the team does this season, sources say.
Hartwig enters his second season as the Steelers starting center since he signed as a free agent in 2008.