Designed voices (voice_…) expire after 1 year: is there any way to keep or recreate one?

Gemini API
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The Voice Design docs say stored voices have “a 1-year TTL” (Voice design), but not what happens at expiry or whether a voice can be kept longer. For any long-lived use (audiobooks, games, series, a brand voice), a voice has to stay identical for years, since new lines are added long after the first ones.

I tested what the API currently allows on gemini-3.8-flash-tts:

  1. Using a voice does not extend it. A prompted voice’s expire_time was exactly create + 365 days. Reads (GET /v1beta/voices/{id}) and synthesis with the voice (generateContent, voiceConfig.voice) left expire_time unchanged, to the nanosecond: immediately, and again 24 hours later.
  2. It can’t be renewed or set. The Voices API has only Create / List / Get / Delete, and expire_time is output-only. store: false is refused for prompted voices.
  3. The same brief does not recreate the voice. Designing the identical brief (same model, gender, language, description) three times gave three different voices. One line spoken with a fixed seed and temperature is byte-identical twice on the same voice, but differs on each of the three, with a clearly different timbre.
  4. Voice design takes no seed. voice.prompted.seed and voice.seed both return 400 Unknown parameter 'seed'.
  5. Nothing portable is returned. GET gives the brief, model, gender, language, sample audio and expire_time, and no embedding or other representation that could be stored and reused.
  6. Replication doesn’t cover it, since it requires a real speaker’s consent recording.

So a designed voice appears to be guaranteed to disappear after a year, with no supported way to bring it back.

Questions

  1. What happens at expire_time? Is the voice deleted, or does synthesis just stop? Is it recoverable?
  2. Is there, or will there be, a way to extend or renew a stored voice (an update method, renewal on use, a longer TTL)?
  3. Is longer or non-expiring retention available on paid tier, Vertex AI or Enterprise?
  4. Will voice design get a seed, so the same brief + seed reproduces the same voice?
  5. Will a voice designed on gemini-3.8-flash-tts keep working, and sound the same, on future TTS models? (Related: designed voices don’t work with gemini-3.8-live.)

Until one of 1–4 has an answer, prebuilt voices (which don’t expire) seem like the only safe choice for anything long-lived, which is a pity given how good Voice Design is.