What changes did Puccini make after Madama Butterfly’s first performance failed?

Following the disastrous opening night of Madama Butterfly at La Scala in 1904, where the audience jeered and mocked the production, Giacomo Puccini withdrew the work to perform extensive revisions.1

The most significant change made by Puccini and his librettists was dividing the opera’s original, overly long second act into two separate acts. This structural adjustment helped improve the pacing and reception of the work. Following these revisions, the opera premiered in Brescia on May 28, 1904, where it achieved great success.1

Puccini continued to refine the score with two additional revisions in 1905 and 1906 before the opera reached its definitive form. Throughout these changes, the famous aria "Un bel dì" remained a central feature of the work.1