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Configuration is the Builder’s home tab: define how your agent behaves, how it opens each conversation, and how it paces its turns. Every edit is saved to the agent’s draft automatically — callers only hear your changes after you publish. New to Agents? Start with the Quickstart.

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System prompt

The system prompt sets the personality, goals, and guardrails that steer every reply. It is capped at 4,000 characters — the Builder stops input at the limit, and the API rejects longer prompts with 422 Unprocessable Entity.
Keep the prompt focused:
  • State who the agent is and what it should accomplish, in a few sentences each.
  • Spell out guardrails explicitly (“If asked about pricing, direct the caller to sales”).
  • Write for the ear — replies are spoken aloud, so ask for short, conversational answers.

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First message

Choose how the agent opens each conversation: first_message and first_message_prompt can each hold up to 10,000 characters. The active mode (first_message_mode: off, fixed, or prompt) decides what callers hear.

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Voice

The Voice panel selects the voice profile your agent speaks with (voice_profile_id) and its speaking language (speaking_language: en, ja, zh, ko, es, fr, de). See Voice & language for picking a voice and how automatic language detection interacts with this setting.

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Conversation settings

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Turn-taking

conversation.eagerness controls how quickly the agent starts talking after the caller stops:
  • relaxed — waits longer, never talks over the caller.
  • balanced (default) — waits for a natural pause.
  • eager — jumps in quickly.

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Interruptions

  • conversation.interruptible (default true) — whether the caller can barge in while the agent is speaking.
  • conversation.interruption_sensitivity — how much caller speech counts as an interruption:
    • low — the agent stops less readily, talking through background noise and short acknowledgements.
    • balanced (default) — interrupts on normal speech.
    • high — the agent stops more readily when the caller speaks, even on brief utterances.

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Call duration

conversation.max_duration_seconds (60–3600, default 1800) ends the session automatically when the limit is reached.
Preview calls in the Builder are capped at 10 minutes or this setting, whichever is lower.

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Recording

conversation.record_audio (default true) — store per-speaker audio for playback and download, with a per-session override on the session request. In the console this lives under your agent’s Settings. Recording defaults to on — make sure callers are informed and consent where your jurisdiction requires it.

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Timezone

conversation.timezone is the default IANA timezone (like Asia/Shanghai) the agent uses for dates and times in conversation. Leave it empty for automatic — each session follows the caller’s device or phone number, falling back to UTC. Set one when your agent serves a single region regardless of who calls. A per-session timezone on the session request overrides this. See Time & timezone for the full resolution order.

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Autosave and publishing

There is no Save button. Each change is written to the agent’s draft moments after you stop editing, and the Saving… / Saved indicator at the bottom-left of the page shows the current state. If a save fails, the Builder tells you and keeps your pending edits so nothing is lost. Drafts never affect live traffic: active integrations keep using the last published version until you press Publish, which snapshots the draft as a new immutable version. The Publish button lights up whenever the draft differs from what is published. See Versions & publishing.

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Configure through the API

The same draft is readable and writable over REST — useful for provisioning agents from your own systems.

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Read the draft

The response also includes the tools, knowledge_base, analysis, and webhooks sections, each covered on its own page. config_hash identifies this draft revision — it changes whenever an edit changes the draft’s content, and a mismatch with the published version is what marks an agent as having unpublished changes.

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Update sections

PATCH takes a partial body and deep-merges it into the draft: send only the sections and fields you want to change, and everything else keeps its value. Fields that hold a list — webhooks.post_call among them — are replaced as a whole, so send the complete list whenever you change one.
The response includes the draft’s new config_hash. Values outside the documented limits — a system prompt over 4,000 characters, max_duration_seconds outside 60–3600 — are rejected with 422 Unprocessable Entity and the draft is left unchanged.

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Config sections

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Going further

Voice & language

Choose a voice profile and control the speaking language.

Versions & publishing

Turn the draft into an immutable live version.

Preview calls

Talk to your draft in the Builder before publishing.

Tools

Let the agent call your backend mid-conversation.