The penalty for the late filing of Form 1065-X (Amended Return or Administrative Adjustment Request) can vary depending on the specific circumstances. As of 2021, the penalty for filing an amended return after the original due date is generally $205 per partner, per month (or part of a month) that the return is late, multiplied by the number of partners in the partnership. However, the penalty can be reduced if the late filing was due to reasonable cause. It is important to consult the official IRS guidance or a tax professional for specific information and advice regarding your situation.