Lyria 3.5 has no edit pass: iterate a music bed for $0.125 a take

Lyria 3.5 cannot be edited after it returns, so iteration means generating again. Google's music generation page, read on 2026-10-05, describes the model as single-turn, with no iterative editing of a finished track. On Sume each accepted generation is a fixed $0.125 through the Music Router, so five takes cost $0.625 and a cap is easy to set.

A disciplined loop

• Take 1: your full brief, written with the seven-axis template.
• Takes 2 to 5: change exactly one axis per take and keep everything else identical, so you know what caused the difference.
• Stop at five. If none works, the brief is wrong, not the dice.
• Use a distinct Idempotency-Key per take, and reuse a key only to retry the same take after a network error.

What not to rely on

The router rejects duration and duration_seconds, and a non-empty negative_prompt returns 400 negative_prompt_unsupported, so exclusions go in the prompt text: "no vocals, no drums". The default sume/music-auto resolves to Lyria 3.5 today and may move without notice; pin lyria-3.5 while you iterate so takes are comparable. job.request.routed_model in the job record shows which engine ran, as explained in Jobs and results.

For reference, Google's pricing page, read on 2026-10-05, lists Lyria 3.5 at $0.08 per song with no free tier, while Sume's $0.125 is the price on a Sume account.