20th and 21st centuries
At the beginning of the 20th century, Gustav Mahler wrote long, large-scale symphonies. His Eighth Symphony, for example, was composed in 1906 and is nicknamed the "Symphony of a Thousand" because of the forces required to perform it. The 20th century also saw further diversification in the style and content of works that composers labeled symphonies (Anon. 2008). Some composers, including Dmitri Shostakovich, Sergei Rachmaninoff, and Carl Nielsen, continued to write in the traditional four-movement form, while other composers took different approaches: Jean Sibelius' Symphony No. 7, his last, is in one movement, whereas Alan Hovhaness's Symphony No. 9, Saint VartanÑoriginally op. 80, changed to op. 180Ñcomposed in 1949Ð50, is in twenty-four.
There remained, however, certain tendencies: symphonies were still almost always orchestral works. Designating a work a "symphony" still implied a degree of sophistication and seriousness of purpose. The word sinfonietta came into use to designate a work that is shorter, of more modest aims, or "lighter" than a symphony, such as Sergei Prokofiev's Sinfonietta (Kennedy 2006; Temperley 2001).
There has also been diversification in the size of orchestra required. While Mahler's symphonies call for extravagant resources, Arnold Schoenberg's two Chamber Symphonies, opp. 9 (1906) and 38a (1906-39), and the Chamber Symphonies by Franz Schreker (1916), George Enescu (1954), Edison Denisov (1982, 1994) and John Adams (1992) are scored for chamber groups.
In the 20th and early 21st century symphonies have been written for wind ensemble and band. Notable examples are Paul Hindemith's Symphony in B-flat for Band from 1951 (Hansen 2005, 95), and Alan Hovhaness's Symphonies No. 4, op. 165, No. 7, "Nanga Parvat", op. 175, No. 14, "Ararat", op. 194, and No. 23, "Ani", op. 249Ñcomposed in 1958, 1959, 1961, and 1972 respectivelyÑwhich are symphonic works for school and college wind bands. Hovhaness is also notable for having written 67 numbered symphonies, whilst Englishman Havergal Brian wrote 32.

Poulenc: Sinfonietta for Chamber Orchestra

Messiaen - TURANGALILA SYMPHONIE

Arnold Schoenberg Chamber Symphony No. 1, Op. 9

ARCHIVIO IEM Stravinsky's Symphony in Three Movements, LSO Valery Gergiev
Stravinsky's Symphony in Three Movements (Part 1¡)
London Symphony Orchestra
Cond. Valery Gergiev

Mahler - Symphony No. 8 - Ending (Rattle, NYOGB)
Simon Rattle and the National Youth Orchestra of Great Britain

Shostakovich: Symphony No. 5 / Bernstein á New York Philharmonic Orchestra
By simultaneously pleasing the authorities with the Fifth Symphony while giving the audience an outlet for their sorrow, Shostakovich showed how effectively he had mastered the essence of the Romantic symphony. Bruckner and Mahler had developed the symphony into a genre working specific musical images and allusions into a network through which each listener could interpret and evaluate on personal grounds. This transcendence of concrete content allowed for variedÑand opposingÑreadings of the musico-emotional content of a symphony while also rendering a definitive account of its meaning impossible. Shostakovich may owe his artistic survival to his mastery of this genre and its now-inherent blurring of boundaries. While satisfying the Soviet demand for monumentality and classicism, it left room for personal expression.[27]

FSU Symphonic Band - Hindemith's Symphony in B-flat - Mvt. 1

Alan Hovhaness Mysterious Mountain I (Andante con moto)