A dedicated chamber musician, Stumpf is a member of Johannes String Quartet and Weiss-Kaplan-Stumpf Trio. He has appeared in chamber music series at Carnegie Hall, Alice Tully Hall, Kennedy Center, Boston Celebrity Series, Da Camera Society in Los Angeles, Walt Disney Concert Hall, Cologne Philharmonic, Concertgebouw in Amsterdam, and Casals Hall in Tokyo. Stumpf has performed with chamber music societies of Boston, Brooklyn, Chicago, and Philadelphia, at Casals Festival in Puerto Rico, and festivals of Marlboro, Santa Fe, Bridgehampton, Ottawa, Portland, Great Lakes, Ojai, and Aspen. He has toured with Music from Marlboro, Casals Hall Ensemble in Japan, and pianist Mitsuko Uchida in performances of the complete Mozart piano trios. He has collaborated with pianists Leif Ove Andsnes, Emanuel Ax, Jorge Bolet, Yefim Bronfman, Radu Lupu, Wolfgang Sawallisch, András Schiff, Jean-Yves Thibaudet, Mitsuko Uchida, and Emerson and Guarneri string quartets. The latter has toured with Johannes Quartet, and premiered commissions from composers William Bolcom and Esa-Pekka Salonen.
Concerto appearances include Boston Symphony, Philadelphia Orchestra, Los Angeles Philharmonic, Boston Philharmonic, Virginia Symphony, Vermont Symphony, Connecticut String Orchestra, Spokane Symphony, Sioux City Symphony, Chamber Orchestra of the South Bay, Aspen Music Festival, and opening concert of the 2012 Piatigorsky International Cello Festival in Los Angeles. Stumpf has performed recitals at the universities of Hartford, Syracuse, and Delaware, Vanderbilt University, Jordan Hall in Boston, and Philips and Corcoran galleries in Washington, DC. He has presented Bach’s complete cello suites on the Philadelphia Chamber Music Society series, and as part of Chamber Music in Historic Sites, Los Angeles. His awards include first prizes at Washington International Competition, Graham-Stahl Competition, and Aspen Concerto Competition, as well as second prize in the Evian International String Quartet Competition.
As a former member of Boston Musica Viva, Stumpf has premiered numerous new works, including those in the microtonal realm. He has taught at Hartt School of Music, New England Conservatory, and University of Southern California. He was also visiting faculty at Curtis Institute of Music, Yellow Barn, and Musicorda Summer String Program. He has conducted masterclasses at Curtis, New England Conservatory, Royal Conservatory of Music in Toronto, Hong Kong Academy for Performing Arts, Manhattan and Mannes schools of music, Seoul National University, Temple University, Vanderbilt University, Pennsylvania State University, and universities of Delaware, Indiana, Iowa, and Michigan.