ElevenLabs model. Turbo/Flash are lower latency; eleven_v3 is required for reliable audio-tag delivery and routes through the non-stream endpoint.
v3 preset mapped to a float on the wire: Creative=0.3, Natural=0.5, Robust=0.8. Ignored for non-v3 models.
Controls how numbers/abbreviations are spoken. 'auto' lets ElevenLabs decide.