Pittsburgh would ship Hanrahan and another player to the Red Sox in exchange for four players, including outfielder-first baseman Jerry Sands and minor league pitcher Stolmy Pimentel. The person spoke on condition of anonymity Saturday because the trade had not been finalized.
The 31-year-old Hanrahan has been one of baseball's best closers the last two years, saving 76 games from 2011-12 and making the NL All-Star team in both seasons. He made $4,135,000 this year and is eligible for arbitration.
Jason Grilli, re-signed by the Pirates this month, would likely step into the closer role next year.