Skip to main content

​
The model catalog

Assistants don’t hardcode providers — they pick from a curated model catalog covering four types: Only the platform admin controls availability. They enable models globally, can grant or block a model for one user, and define which engine modes each model supports. Tenant admins cannot override the catalog. With the Fallbacks & Guardrails add-on, the assistant editor shows provider and model selectors. Pipeline, realtime, and half-cascade keep independent choices. Choosing the default stores null, so later admin changes take effect automatically:
  1. Assistant selection (Fallbacks & Guardrails only)
  2. Personal default set by the platform admin
  3. Platform default
  4. Safe runtime fallback
Without Fallbacks & Guardrails the editor remains automatic. Personal admin defaults still apply. Unavailable legacy values remain visible so they can be reset, but cannot be selected again.
Look for the Recommended badge — those are the models we test most and tune defaults for. Low latency flags models suited for snappy phone conversations.

​
The voice library

The voice picker loads the complete paginated catalog from every enabled TTS provider, filterable by language and gender, with instant audio previews — click play to hear a sample before committing. ElevenLabs voices with custom rates or credit multipliers are excluded, so every ElevenLabs voice shown in the picker uses the provider’s standard voice rate.
  • Voice per assistant — the default speaking voice.
  • Voice override per flow agent — individual flow agents can speak with a different voice (e.g. a distinct voice for the “sales specialist” agent).
  • Voice per language — with automatic language switching, you map a voice per language so the assistant switches voice together with language.
  • Cloned voices — with the Clone your own voice add-on (or Include free on the plan), you can add custom clones and use them like any library voice. A clone is private to the account that created it: other members of the same workspace cannot see or select it. Capacity is limited by max_cloned_voices.

​
Speaking style

Pipeline and half-cascade assistants use the same provider-aware voice controls. The editor only sends settings supported by the resolved TTS model:
  • Cartesia Sonic 3 / 3.5 — speaking rate, output volume, and optional dynamic emotion cues.
  • Eleven v3 — stability and native audio-tag expressiveness. Unsupported speed, similarity, style, and speaker-boost controls are not sent.
  • Other supported ElevenLabs models — speaking rate, stability, similarity, style exaggeration, and speaker boost.
  • OpenAI and Gemini TTS — free-text speaking-style instructions when the selected model supports them.
  • Pronunciation dictionary — per-assistant key-value mapping, e.g. "API" → "A P I" or your company name spelled phonetically. Applied to all spoken output.
  • Markdown & emoji filters — enabled by default so LLM formatting artifacts are never read aloud.
Changing any effective voice control also changes the phrase-cache key, so cached greetings and filler phrases cannot reuse audio produced with older settings.

​
Fallback chains (Fallbacks & Guardrails)

For production reliability you can define a fallback chain per stage: if the primary provider degrades mid-call, the engine switches to the next entry — the call continues seamlessly.
  • STT — e.g. Deepgram nova-3 → AssemblyAI universal-streaming
  • LLM — e.g. GPT → Groq
  • TTS — e.g. Cartesia sonic → ElevenLabs (each entry may specify its own voice)
Provider health changes are logged as call events, so you can see afterwards whether a fallback fired. Fallbacks are a plan-gated feature.
Even without configured fallbacks, a broken configuration never kills a call: the engine falls back to a safe default stack and records a config_error event.