---
title: Webhook Tool Filler Messages for Telnyx AI Assistants
canonical: https://telnyx.com/release-notes/webhook-tool-filler-messages
---
# Webhook Tool Filler Messages for Telnyx AI Assistants

[Release notes](https://telnyx.com/release-notes)

# Webhook Tool Filler Messages Now Available for Telnyx AI Assistants

### 6, Jul 2026

AI Assistants can now speak scripted utterances at the start of a webhook tool call and during long-running requests. Callers stay engaged while the assistant waits on an external API, database lookup, or third-party model, instead of sitting in silence.

### What's new

* **Filter messages on webhook tools:** Set the exact phrase the assistant speaks when a synchronous webhook starts, and tier additional phrases at delay thresholds (5s, 10s, 15s) while the call is still executing.
* **Deterministic utterances:** Messages are scripted per tool, not LLM-improvised on the fly. You control wording, timing, and brand voice for every wait state.
* **Sync webhook and MCP tool support:** Filler messages apply to synchronous webhook tool calls and MCP tool calls where the assistant holds the line until the response returns. Async webhooks are not supported.

### Why it matters

Silence is where voice AI calls die. A webhook tool call that takes 8 to 12 seconds for a database lookup or third-party API leaves the caller staring at dead air, and on a phone call that reads as broken, not loading. Most voice platforms either go silent and lose the caller, or ask the LLM to improvise filler, which rambles, drifts off-brand, and can't be tuned.

This lets you script the wait-state UX the same way you script the conversation flow. "Let me look that up for you" at the start, "still working on this" at 5 seconds, "almost there" at 15 seconds. Deterministic, tiered, and per-tool. The same control you have over the conversation now extends to the gaps the conversation depends on.

### Example use cases

* Customer support agents that query a billing or CRM system mid-call can acknowledge the lookup and reassure the caller instead of going mute.
* AI receptionists booking appointments through a scheduling webhook keep the caller on the line with timed acknowledgments while the calendar API responds.
* Voice agents calling slow third-party LLMs or RAG pipelines can set longer delay tiers to match realistic execution times without callers assuming the call dropped.

### Getting started

1. In Mission Control, open AI, then Assistants, and select your assistant.
2. Go to the Webhook Tools section and edit or create a webhook tool.
3. Select Sync as the Request Mode.
4. Open the Filter Messages tab.
5. Add a message for "When the request starts" to set the opening utterance.
6. Add delay-tiered messages with a delay in milliseconds for each mid-call phrase.
7. Save the tool.

Each filler message has a `type` of `request_start` (spoken immediately when the tool call begins) or `request_response_delayed` (spoken after `timing_ms` milliseconds if the response has not yet arrived). The `timing_ms` field accepts 100 to 120000 ms and is only required for delayed messages. Once the response arrives, any remaining delayed messages are skipped.

{
  "filler_messages": [
    { "type": "request_start", "content": "Let me look that up for you." },
    { "type": "request_response_delayed", "content": "Still working on this.", "timing_ms": 5000 },
    { "type": "request_response_delayed", "content": "Almost there.", "timing_ms": 15000 }
  ]
}

**Learn more** in the [AI Assistants docs](https://developers.telnyx.com/docs/inference/ai-assistants) or the [Telnyx docs](https://developers.telnyx.com).

[Start building](https://telnyx.com/sign-up)

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