May 4, 2026

Aura-2 TTS voices now support runtime speed and pronunciation controls in English and Spanish, available on both batch and streaming WebSocket endpoints. Together, these controls give developers finer-grained tools to improve naturalness — tuning pacing and correcting pronunciation to match their needs.

Speed control adjusts the speaking rate of generated audio while maintaining natural prosody, with a supported range of 0.7x–1.5x. For Spanish voices, the recommended range is 0.9x–1.5x; values below 0.9x may introduce disfluencies.

Pronunciation control overrides the default pronunciation of specific words using inline IPA notation, e.g. The patient was prescribed \{"word": "dupilumab", "pronounce": "duːˈpɪljuːmæb"\}.

See Voice Controls for details.

These controls are also supported when using Aura-2 inside the Voice Agent API: set speed once at the session level, and have the LLM emit pronunciation overrides inline. See Voice Agent TTS Controls for the recommended setup.

These controls are powered by an updated Aura-2 voice-pack model. Self-hosted deployments using a voice-pack from before the April 2026 release will return 400 Bad Request on requests including speed or pronounce parameters. See the April 2026 self-hosted release notes for voice-pack version requirements and upgrade instructions.