Which opera  Pelléas et Mélisande and Die schweigsame Frau has fewer acts ?
Die schweigsame Frau Die schweigsame Frau ("The Silent Woman"), Op. 80, is a 1935 opera in three acts by Richard Strauss with libretto by Stefan Zweig after Ben Jonson's "Epicoene, or the Silent Woman".
Senza sangue Senza sangue (Without blood) an opera in one act by Péter Eötvös with a libretto by Mari Mezei. It is based on the second part of the novel of the same name by Alessandro Baricco and is intended to be performed jointly with Béla Bartók's one-act "Bluebeard's Castle". The concert première was given by the Cologne Philharmonic Orchestra on 1 May 2015. It was premièred in full on 15 May 2016 at the Festival d'Avignon. It is his tenth opera. Anne Sofie von Otter, who gave the New York première with the New York Philharmonic, said: "“The piece is not at all easy for the two singers... [It’s] hard to find the pitch; you have to work it into the voice, unless of course you happen to have perfect pitch, which I don’t."