All data sources on the terminal allow you to use them for free. The only thing needed is you signing up on their page to get an API key.

https://docs.openbb.co/terminal/quickstart/api-keys

After that your API key will allow you limited usage, e.g. AlphaVantage allows 5 requests per minute. This means that if you want more access you'll have to subscribe to one of their premium tiers.