> ## Documentation Index
> Fetch the complete documentation index at: https://docs.nixflex.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Update agent

> PUT /v1/agents/:id

Updates an agent's configuration. Only include fields you want to change — omitted fields keep their current values.

## Request

```bash theme={null}
curl -X PUT https://api.nixflex.com/v1/agents/agent_125207e452f8714a \
  -H "Authorization: Bearer KEY_ID:KEY_SECRET" \
  -H "Content-Type: application/json" \
  -d '{
    "welcome_message": "Hi, Acme Dental, how may I help you today?",
    "response_length": "short"
  }'
```

## Body parameters

Any field from [Create agent](/api-reference/agents/create) can be updated. Pass only the fields you want to change.

## Response

`200 OK` — returns the updated agent object.

## Behaviour

* **Active calls are unaffected.** Updating an agent while a call is in progress doesn't change behaviour mid-call. New calls use the new config.
* **`agent_id` and `api_key_id` are immutable.** Trying to change them is ignored.
* **No partial validation.** If you submit an invalid value for any field, the whole update fails.

## Errors

| Code               | Cause                             |
| ------------------ | --------------------------------- |
| `agent_not_found`  | ID doesn't exist or isn't yours   |
| `prompt_too_long`  | New `system_prompt` exceeds limit |
| `invalid_voice_id` | Voice not supported               |