Does Clearbit data update automatically?

Yes - Clearbit data is automatically researched whenever a lead/contact/account is created, even if the record is not manually opened by a user. This happens through a Salesforce background job.

In order to trigger a lead to enrich when it is opened, you will need to include our VisualForce widget on the page layout. Don't have the real estate? Simply set the widget to 1px by 1px. That way, the enrichment will be triggered when the lead is viewed, and your Salesforce team won't even know the widget is there.