Hi,
There is no limit on the number of lists you can create in an account. I would advise against creating thousands of lists, however, since an account can become unresponsive due to loading a lot of data associated with lists. I would try to keep the number of lists in an account in the hundreds if possible, either by periodically removing lists that aren't being used, or re-using lists.
Best Regards,
Shannon W.
API Support Specialist
