The person spoke to The Associated Press on Friday night on condition of anonymity because the deal had not been completed yet.
Haren, a three-time All-Star from 2007-09, is the second starting pitcher traded by the busy Angels in three days. Los Angeles shipped Ervin Santana to the Kansas City Royals on Wednesday for minor league left-hander Brandon Sisk.
The Angels had until midnight EDT on Friday to exercise Haren's $15.5 million option for next season. He had a $3.5 million buyout. The right-hander was 12-13 with a career-worst 4.33 ERA this year and spent time on the disabled list for the first time.
The Cubs declined to comment.
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AP Sports Writer Ronald Blum contributed to this report.