Mancini, who has been in the lineup at designated hitter 51 times this season, also could fill that role for the AL West leaders with Michael Brantley out indefinitely with a shoulder injury.
The 30-year-old Mancini is hitting .268 with 10 homers and 41 RBIs in 92 games this season. He broke into the majors with Baltimore in 2016 and batted .270 with 117 homers and 350 RBIs in 701 games with the Orioles.
“I always said I wanted to see the rebuild through and I feel like, in a lot of ways, I have,” Mancini told reporters in Arlington, Texas where the Orioles were playing the Rangers on Monday night. “I think things are only going to get better here, and besides when I’m playing against them, I’m always gonna be rooting for these guys in here.”
Houston also received minor league right-hander Jayden Murray from Tampa Bay. The Astros sent Siri to the Rays and minor league right-hander Chayce McDermott to the Orioles.
The 27-year-old Siri made his big league debut last year. He hit .178 with three homers and 10 RBIs in 48 games with Houston this season.
Mancini has a $7.5 million salary this season as part of a contract that includes a $10 million mutual option for 2023 with a $250,000 buyout.
AP Baseball Writers Ron Blum and Stephen Hawkins contributed to this report.