Strobes uses Threat Intel data to associate real-world risk to each vulnerability. By default, Strobes is equipped with XO Intel which is a homegrown TI service by the Strobes team. This is free to use.
In case you would like to use any 3rd party threat intel such as Intel Graph or any other source, you have the choice of selection.
However, at any point, only one Threat Intel service could be used. For this, you are required to provide the threat data query frequency and also API key if needed.