The person says compensation issues must be worked out before the deal is finalized. The person spoke on the condition of anonymity Wednesday night because there has not been an announcement.
The 37-year-old Epstein would leave the Red Sox with a year remaining on his contract as general manager and take over what is expected to be an expanded role with the Cubs, who have gone 103 years without a World Series championship.
Radio station WEEI in Boston, ESPN the Magazine and SI.com earlier cited unidentified sources in reporting that Epstein has agreed to a five-year deal.
The Cubs declined comment Wednesday and Red Sox officials could not be reached by The Associated Press. On Tuesday, a person familiar with the situation told the AP that Epstein was likely to join the Cubs within 48 hours.