On November 5, 2018 the Office of Foreign Assets Control (OFAC) began to re-impose several sanctions on Iran related to the 180-day wind-down period and the reimposition of US sanctions that had been lifted or waived in connection with the Joint Comprehensive Plan of Action (JCPOA).
The biggest change you will see is that over 700 people have been designated or identified and added to the SDN list, including those that had been recently removed from the list in connection with JCPOA. In addition, person and associated block property that was previously identified on Executive Order (EO) 13599 have been moved to the SDN list and OFAC has removed EO 13599 from its website.
An amendment to the Iranian Transactions Sanctions Regulations (ITSR) has taken affect and will reimpose certain sanctions pursuant to EO 13846 and technical changes that remove references to EO 13599.
OFAC Frequently Asked Questions: https://www.treasury.gov/resource-center/faqs/Sanctions/Pages/faq_iran.aspx#630