In 1989, Summers began his tenure as the music director of the San Francisco Opera Center, a training program for young singers; his first mainstage production, Die Fledermaus, was in 1990.
Other highlights include collaborating with André Previn on the 1998 world premiere of A Streetcar Named Desire and conducting several of the performances; serving as principal guest conductor from 1999 through 2016; conducting Jake Heggie's Moby-Dick, which was recorded and telecast on PBS's Great Performances; and in 2015 receiving the San Francisco Opera Medal, the company's highest honor.
Since 1998, Summers has conducted over 60 productions at Houston Grand Opera, including eight world premieres (notably Jake Heggie's It's a Wonderful Life,[6] The End of the Affair, Three Decembers, and Carlisle Floyd's Cold Sassy Tree[7]).
He has since appeared at Barcelona's Gran Teatre del Liceu, most recently conducting La favorite (2018) after his house debut in La Cenerentola, the Welsh National Opera (Rigoletto), the Bregenz Festival (The Magic Flute and Carlisle Floyd's Of Mice and Men), Lisbon's Teatro Nacional de São Carlos (Ariadne auf Naxos), the Opéra national de Bordeaux (Don Pasquale and La bohème), and the European premiere of André Previn's A Streetcar Named Desire at the Opéra national du Rhin in Strasbourg.
Throughout his career, Summers has worked with composers Jake Heggie (Dead Man Walking, The End of the Affair, Three Decembers, Moby-Dick, Great Scott, and It's a Wonderful Life); Carlisle Floyd (Prince of Players and Cold Sassy Tree); Ricky Ian Gordon (The House without a Christmas Tree and A Coffin in Egypt); André Previn (A Streetcar Named Desire and Brief Encounter); Christopher Theofanidis (The Refuge and Heart of a Soldier[11]); Daniel Catán (Salsipuedes); Lee Hoiby (The Tempest); Tod Machover (Resurrection); Paul Moravec (The Letter); Rachel Portman (The Little Prince); Mark Adamo; Michael Daugherty; and R. Murray Schafer, among others.
In 2019, it was announced that Summers would become the co-artistic director of the new Aspen Opera Theater and VocalARTS alongside soprano Renée Fleming starting in 2020.