No, there are no hard limits on the number of items that may be downloaded via our API. Nevertheless, a reasonable and customary rate limit remains in place to ensure equal access to the API for all users, and we continue to ask users to use our service responsibly. We understand the need to be flexible and continue to monitor usage and consult with researchers. We reserve the right to deactivate any API key, however, if we believe usage is abusive or impacting the stability of our systems.