The documentation page for the Register Phone Call API endpoint claims that it's possible to set per-call agent overrides for things like voice_id, etc: https://docs.retellai.com/api-references/register-phone-call#body-agent-override However, when I attempt to do this, the overrides are never applied and the voice I get on the actual call is always the default voice configured on the agent. I'm using the Python SDK, but for clarity, I captured the final request body that gets sent in the

POST /v2/register-phone-call

request and it looks like this:

{
  "agent_id": "agent_8c6f9263fd3c9a8d1036e14f57",
  "direction": "outbound",
  "from_number": "+17164513819",
  "metadata": {
    "agent_id": 1,
    "result_uuid": "70668c59-ac41-4f24-8d09-5ffc61614bf2"
  },
  "retell_llm_dynamic_variables": {
    "prompt": "## Style Guardrails ..."
  },
  "agent_override": {
    "agent": {
      "voice_id": "11labs-Adrian"
    }
  }
}

I've tried this in

retell-sdk@4.36.0

using

extra_body={"agent_override": ...}

as well as in

retell-sdk@5.3.0

by passing the new-ish

agent_override=...

arg directly to

client.call.register_phone_call

- not that it matters, since both just add the

"agent_override"

key to the request body. Thanks in advance! @Omar Ashraf | Community Lead

Hello @Irfan , can you share a call id ?

Of course; here are a few from my testing today:

2025-12-19 10:20:11.455399+00:00 call_c0935fa65dc2f9917cf78dde43c
2025-12-19 10:17:27.060485+00:00 call_05f16045ec667662c4154af85c9
2025-12-19 10:15:15.354318+00:00 call_fc4457b2f72b181fed9582d23e9
2025-12-19 10:09:51.233294+00:00 call_b1a59f8ff6708047a0995decae6

what settings did you try to override ?

The voice id. Please refer to the request payload sample I provided above (note the

"agent_override"

key)

Hello @Irfan , I have reported that to the team I will update you soon,Thanks.

Thanks Omar

@Omar Ashraf | Community Lead , I'm also having issues using this option. I would like to override the response engine

A fix is being pushed in an hour