The penalty for late filing of Form W-8ECI (Certificate of Foreign Person's Claim That Income Is Effectively Connected With the Conduct of a Trade or Business in the United States) depends on the specific circumstances. As of this writing, the penalty for failing to provide a timely and valid form to a withholding agent can result in a withholding tax being applied to certain transactions at a default rate of 30%. It's important to note that tax laws and penalties can vary based on individual circumstances and jurisdiction. It is recommended to consult with a tax professional or the appropriate tax authority to obtain accurate and up-to-date information regarding penalties for late filing of Form W-8ECI.