Get an API KeyUsing 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.
You should never expose your API key to client codeIf 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: 
curl --request GET \
--url https://api.ultravox.ai/api/calls \
--header 'X-API-Key: aBCDef.123456'

​
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:
LevelAPI Requests per Second
Account500
API Key200

​
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 TypePer SecondPer Minute
Free / PAYGO530
Pro10120
Scale30360
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 TypeConcurrency CapPriority Access
Free / PAYGO5 calls❌
ProNo hard cap*❌
ScaleNo 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.