Text-to-speech models
The three Chorus models that synthesize speech, and where Symphony fits instead.
Three models synthesize speech from text. They share a request shape and differ in where the voice comes from.
| Model | model | Voice source |
|---|---|---|
| Chorus Voices | chorus-voices | Nine built-in speakers |
| Chorus Clone | chorus-clone | 47 shipped voices, or one cloned from reference audio you send |
| Chorus Design | chorus-design | A voice synthesized from a written description |
Voices has the request shape for each.
The chorus alias
chorus routes to the preset and cloning models, so
GET /v1/audio/voices?model=chorus returns all 56 of their voices at once. It
does not appear in GET /v1/models, where the three models are listed
separately; send chorus anyway rather than checking it against that catalog.
The model field is case-insensitive.
Voice design is the exception: set "model": "chorus-design" explicitly. Sent
to chorus with instructions and no voice, a request synthesizes the
default speaker and the description designs nothing.
Parameters
| Parameter | Notes |
|---|---|
input | The text to speak. Required. |
voice | A preset id. Non-preset ids are rejected. |
instructions | Style guidance on a preset, or the voice description on chorus-design. |
response_format | mp3, opus, flac, wav, or pcm. |
speed | Speaking rate multiplier, 0.25 to 4.0. |
language | Output language. See supported languages. |
stream_format | sse or audio. Omit to buffer the whole clip. |
ref_audio | Inline data: URL of reference audio, on chorus-clone. |
ref_text | Transcript of the reference audio. |
cache_salt | Prefix-cache isolation key, overwritten when ref_audio is present. |
REST has types, requiredness, and error codes.
Symphony
Symphony is not available on /v1/audio/speech; the endpoint returns a 400
pointing at /v1/chat/completions. Use /v1/chat/completions for its text
turns, or a session at wss://api.sprag.ai/v1/realtime?model=symphony for its
speech, covered under realtime.
The model catalog carries the live list with per-model detail, and pricing has the current rates.