All shares of Regeneron's common stock owned by Sanofi now or in the future are subject to a lock-up provision that prohibits any sales until December 20, 2020;
Pursuant to the January 2018 Letter Agreement, Regeneron agreed to grant a limited waiver of the "lock-up" in the Amended and Restated Investor Agreement so that Sanofi may sell up to an aggregate of 1.4 million shares of Regeneron common stock to fund certain funding obligations under the IO and Antibody Collaborations through the quarterly period ending September 30, 2020.
To date, approximately 530K shares have been purchased by Regeneron from Sanofi; ~870K remaining shares may be sold by Sanofi and purchased by Regeneron (if it elects to do so) under this arrangement.