Opus 5.5 tested on music: agent skill rewrites melodies into virtuosic showpieces
doodlestein · x · 2026-09-24
The author tested Anthropic's Opus 5.5 on their homegrown AI music theory system, mtdt (an agent-facing tool with a skill library). Previous experiments mostly used GPT-6 Astra; Opus 5.5 was chosen for its much lower cost, and it proved very capable at musical tasks.
The demo used a newly written skill: take a simple melody as input and rewrite it in an over-the-top virtuosic style, modeled on Horowitz's Carmen Variations. Given "Anne's Theme" from the 1985 Anne of Green Gables film, Opus 5.5 produced an "Ultra-Schmaltzy" Horowitz-meets-Liberace version — with the system verifying playability by a real human pianist. The author judged it did a yeoman's job while noting the original remains musically better; the test was about how far the system could push while preserving the piece's essential character.
Related event: Devs Test Opus 5.5 on Music Theory: Strong and Cheaper(2 posts)→
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