Thank You for reaching out. There are rate limits for the API's that you can consume from the sandbox, but we have kept the limits at optimal levels enabling you to test Visa Developer Center API's from your applications.
Thanks for your inquiry and your interest in Visa Developer. Talking among the team here we wanted to give you more detail.
One assumes you mean throughput rates for individual APIs? In the production gateway, there is no preset rate for the VDP gateway nor for individual APIs in most cases, but each API will have different throughput characteristics, as you might expect.
Some APIs have preset rates built into their license structure, where the application's throughput is built into the API license fee. You'll know that long before you go to production if it applies to an API in your application.
When requesting your application to be moved to production, the throughput characteristics for your application are part of the Q&A. That information is used in part to ensure the VDP infrastructure and APIs have sufficient resources to accommodate the load across all clients.
Last, please note that the above applies to production traffic; the VDP Sandbox is not designed to model throughput. If someone starts driving high traffic volumes to the sandbox they will be asked to reduce it, or if needed their transaction rate may be throttled administratively.