Is there an API for Flows?

Yes, in two ways:

• Run a flow you built in the app. Publish the flow as a template, and you can run it through the API with your own input values, for example to connect a CMS to a flow for automated content generation. See the Templates quickstart.
• Build the chain in code. The Image & Video API runs one generation per call, the equivalent of one node in a flow, and each generation can take a previous one as a reference. Your code decides which models to call and in what order, so it can assemble a different chain for each request. See Chain one generation into the next.