Ultravox REST API Overview
Using the Ultravox API requires an API key.
You can sign-up for a free account that comes with 30 free minutes for creating calls.
Base URL
The Ultravox API is available at https://api.ultravox.ai/api/.
API Keys
Ultravox API keys are 41 characters long and are made up of two alphanumeric parts separated by a period. The first part is 8 characters long and the second is 32 characters.
For example: Zk9Ht7Lm.wX7pN9fM3kLj6tRq2bGhA8yE5cZvD4sT
Throughout the docs we use aBCDef.123456 for brevity.
X-API-Key Header
When making API calls, pass your key in using the X-API-Key header.
If you really want to ignore this advice for a local demo, use the X-Unsafe-API-Key header instead at your own risk. It works the same way except that our server will allow it in CORS preflight requests.
Here’s an example showing how to use the fictional API key aBCDef.123456 to get a list of calls:
Rate Limits
The Ultravox API includes safeguards to help maximize stability for all customers. Too many API requests can trigger an error with status code 429. See Scaling & Call Concurrency for more information on 429 errors and how to properly handle them.
API Limits
We restrict the number of total API requests per second. This restriction applies to all API endpoints that are part of https://api.ultravox.ai/api/.
We restrict at the account and API key level as follows:
| Level | API Requests per Second |
|---|---|
| Account | 500 |
| API Key | 200 |
Call Creation Limits
In addition to the overall API limits above, we place additional restrictions on how quickly accounts can create calls in the system.
| Plan Type | Per Second | Per Minute |
|---|---|---|
| Free / PAYGO | 5 | 30 |
| Pro | 10 | 120 |
| Scale | 30 | 360 |
Call creation is limited by whichever threshold is reached first (per second or per minute).
Call Concurrency Limits
The number of concurrent calls allowed depends on your plan.
| Plan Type | Concurrency Cap | Priority Access |
|---|---|---|
| Free / PAYGO | 5 calls | ❌ |
| Pro | No hard cap* | ❌ |
| Scale | No hard cap* | ✅ Up to 100 |
*Still subject to infra limits under extreme load.
See Scaling & Call Concurrency for more details on how call concurrency works in Ultravox Realtime.
Playground
If you want to quickly experiment with prompts and voices, the fastest way to do that is in the Ultravox Dashboard.
You can also paste in an Ultravox API key throughout the API reference (look for “Authorization” and paste your key where it asks for X-API-Key) and test the REST API endpoints.