Epstein's contract as Red Sox general manager and executive vice president runs through 2012, but WEEI radio in Boston reported Wednesday that a five- year deal worth $15 million had been reached. The report said the sides hadn't decided what title Epstein will have.
ESPN also reported that Epstein and the Cubs agreed to a five-year deal.
The change would abruptly end Epstein's remarkable run as Red Sox general manager.
In 2002, Epstein became the youngest GM in major league history when he took over the Red Sox at age 28. He assembled the 2004 squad noted for ending an 86-year championship drought in Boston and tacked on another World Series title three years later. He took on the additional role of executive vice president in 2006.
This past season the Red Sox fell apart down the stretch, finishing 7-20 in September to squander a nine-game lead in the AL wild card race to the Tampa Bay Rays. The collapse resulted in manager Terry Francona parting ways with the franchise shortly after the season.
The Cubs have not won a World Series title since 1908. They went 71-91 this past season, missing out on the postseason for the third straight year. General manager Jim Hendry was fired in mid-August, and Randy Bush was promoted from assistant to interim GM.