At about 45 minutes, Beethoven’s ‘Hammerklavier’ Sonata, Op. 106 was the longest solo piano composition of its day (1818), while the longest piano concerto seems to be Busoni’s five-movement monster, lasting around 73 minutes.
But these fade into oblivion compared with the works of Kaikhosru Shapurji Sorabji (1892-1988) who penned more piano marathons than any other. The most famous (or notorious depending on your view) is his Opus Clavicembalisticum (around four hours). His 100 Etudes transcendantes would take seven hours to perform – nothing compared with his Symphonic Variations for Piano at an estimated, leisurely nine hours.
Even these are short hauls against the daunting ten hours of Frederic Rzewski’s The Road and Jacob Mashak’s work for two pianos, Beatus Vir, which clocks in at around 11 hours. If one were to include repetitive solo piano works, then even Mashak must yield to Satie’s Vexations which consists of a 52-beat unbarred idea (marked ‘Très lent’) played a seemingly random 840 times. A performance lasts a little over 20 hours.