Pedro Sánchez Gil with Claude Opus 5.5, 2026
Bach, Mozart, Beethoven and Schubert each left music that stops mid-thought: a fugue that breaks off soon after it spells its composer’s name, a Lacrimosa that ends after eight bars, a sonata with a blank page where the development should be. Claude Opus 5.5 read the manuscripts note by note and finished ten of them in the composers’ own language.
Black ink is theirs; blue ink is the machine’s. Every recording lets you hear the seam, the moment one hand stops and the other begins. After the ten completions come new pieces from the same collaboration: a fifth Season for Vivaldi, two movements of Mozart’s Requiem grown longer, an elegy and a fugue.
The end of Bach’s manuscript of The Art of Fugue, on the organ. Its third subject spells his name, BACH. Soon after all three subjects sound together for the first time, the page stops, and the blue notes begin.
Each score is a picture of its recording: time runs left to right, pitch from low to high. Click anywhere on one to listen from there.
Chosen for how much survives and how much is missing: from a bar and a half of a chorale prelude to 239 bars of The Art of Fugue.
No. 1Johann Sebastian Bach
BWV 1080. Leipzig, late 1740s
Left239 bars. The manuscript breaks off just after the three subjects sound together for the first time. The third one spells his name: B flat, A, C, B natural.
Added56 bars. The fourth subject, the main theme of The Art of Fugue, joins the other three, as Gustav Nottebohm showed in 1881 that it could.
No. 2Wolfgang Amadeus Mozart
K. 626. Vienna, 1791
LeftEight bars of the Lacrimosa: the violins for two bars, then the choir and the bass. On a separate sketch leaf, sixteen bars of an Amen fugue.
AddedThe orchestra, the rest of the Lacrimosa, and a whole Amen fugue grown from his sketch. His sketched bars come back in black ink at 2:47.
No. 3Wolfgang Amadeus Mozart
K. 626, sketch leaf. Vienna, 1791
LeftSixteen bars on a sketch leaf now in Berlin: a fugue whose subject is the Requiem's opening theme turned upside down.
AddedThe rest of the fugue, for organ.
No. 4Franz Schubert
D 759. Vienna, 1822
LeftNine bars in full score, then only a piano sketch: the whole Scherzo, and the first half of the Trio's melody with no harmony.
AddedThe orchestra from bar ten on, harmony for the Trio and its missing second half, and the return of the Scherzo.
No. 5Wolfgang Amadeus Mozart
K. 396 (385f). Vienna, 1782
Left27 bars: a complete exposition. The violin waits until bar 23 to enter.
Added60 bars: the development and the recapitulation.
No. 6Wolfgang Amadeus Mozart
K. 516c (Anh. 91)
Left93 bars in all five parts: the exposition and the first bars after it.
Added145 bars, to the end of the movement.
No. 7Johann Sebastian Bach
BWV 906/2. Leipzig, about 1738
Left47 bars and a single chord: a deceptive cadence onto A flat, and then nothing.
Added50 bars, with the middle entries, stretto and pedal point Bach's text never reached.
No. 8Ludwig van Beethoven
WoO 62. Vienna, November 1826
Left24 bars of an Andante maestoso, known only from Diabelli's piano arrangement of 1838.
AddedThe string quintet he had in mind, and the rest of the movement.
No. 9Johann Sebastian Bach
BWV Anh. 200. Weimar, 1710s
LeftA title, a tempo (molt' adagio) and a bar and a half. The rest of the page is empty.
AddedThe whole chorale prelude, one statement of each of the hymn's five phrases.
No. 10Franz Schubert
D 655. Vienna, April 1819
Left73 bars: the exposition, a repeat sign, and a blank page.
Added116 bars: the development and the recapitulation.
The same collaboration with no manuscript to finish. Each piece began as one sentence from Pedro, printed above it the way a score prints its tempo marking.
“Make a fifth Vivaldi season. Surprise me.”Pedro’s brief
A fifth Season, concerto in D major for violin, strings and harpsichord
In Vivaldi's Venice the year really had a fifth season: masks were legal for close to half of it, and the opera calendar he worked by had a Carnival season of its own. The concerto follows a new sonnet, as the Four Seasons do. An acrobat flies down from the Campanile, a tower of men is built and falls, a masked lover sings to a beloved who cannot answer, and the last night's dance is stopped by the midnight bell.
Vivaldi printed a sonnet with each Season and set its letters in the score, beside the music that depicts each line. This one is new. Choose a line to hear its music; while the concerto plays, the line it is depicting lights up.
“Keep its epicness, but add more, so the new parts are surprisingly unique and consistent with the rest.”Pedro’s brief
Mozart, Requiem K. 626: 22 bars become 45
Every one of Mozart's 1,886 notes stays in place. Between “salvas gratis” and “salva me” come a hushed prayer on the chant tone of the Requiem's own Introit, a double fugue with the Requiem's opening theme in the trombone, a storm on “tremendae”, and a “Rex!” on a chord nobody expects. Then a bar of silence, and Mozart's own ending.
“Especially the motif of Quam olim Abrahae. That part is very powerful.”Pedro’s brief
Mozart, Requiem K. 626: the Quam olim Abrahae fugue grows from 35 bars to 51
Just before Mozart's final cadence, the music swerves to E flat. The subject is sung upside down over a hushed chorale, then at half speed by three trombones, then the whole choir sings its opening on a diminished seventh and falls into the dominant. Mozart's last stretto returns, and his own cadence ends it. All 6,041 of his notes are where he put them.
“Very, very somber and sorrowful. Nostalgic of a future that never realized.”Pedro’s brief
For orchestra
A slow lament in F minor for woodwinds, horn, three trombones, timpani and strings, 40 bars long. The first orchestral piece of the project, with every note written out in the score.
“Compose and direct a fugue like Bach, grounded in music theory, that is beautiful.”Pedro’s brief
Three voices, in the manner of Bach
The first piece of the project, in 21 bars: a subject, a tonal answer, an invertible countersubject, middle entries in E flat major and F minor, a dominant pedal, and a coda over a tonic pedal that ends in C major. Heard three ways.
The same eight steps for every piece. The boxed letters are rehearsal marks, the signs a conductor uses to say where to start.
Every piece began as a line from Pedro: a mood, a dare, a fragment worth finishing. The direction stayed Pedro's: what to attempt, what landed, what to push further.
“Nostalgic of a future that never realized.”
A research pass through catalogues, sketch studies and editions found melodies and movements the great composers began and abandoned. Ten were chosen for how much survives and how much is still missing.
Bach, Mozart, Beethoven, Schubert
Public-domain editions and manuscripts only: the Bach-Gesellschaft, the nineteenth-century complete editions of Mozart and Schubert, the Neue Mozart-Ausgabe, Mozart's sketch leaf, the Vienna delivery score of the Requiem, Schubert's autograph facsimile.
IMSLP and the Mozarteum's Digital Edition
Scanned pages were read staff by staff with a notehead scanner, then checked by eye against a second source where one exists; The Art of Fugue comes from a scholarly encoding of the Bach-Gesellschaft text. Where sources disagree, the doubt is written down instead of guessed away.
Mozart's Amen sketch: its barlines counted one by one on the facsimile, sixteen bars
The composer's notes are sacred: a script compares every note before the seam with the source and fails on a single difference. The new music must pass a counterpoint check, with no parallel fifths or octaves between independent voices.
0 differences, in all ten completions and both extensions
Each completion develops the composer's own motives in the forms and harmony of the time: Bach's three subjects meet the main theme of The Art of Fugue; the Quam olim subject is inverted and augmented, as a fugue of 1791 would do.
24,898 notes in blue ink on this page
A rendering engine plays the scores with recorded instruments, all public domain, and a conductor: tempo, breaths, fermatas, balance. Phrases swell toward their peak, dissonances lean, leaps arrive a little late, leading tones lean sharp.
VSCO-2 and VCSL samples: orchestra, organ, upright piano, an Italian harpsichord
Every recording is checked by machine before anyone hears it: the pitches of every beat against the score, clicks, loudness, the soloist's balance against the orchestra. Then by ear, and then the next sentence from Pedro.
Main pitch present in 87 to 97% of beats, 0 clicks
Fine