Correction from 10/9/2019: I thought the patent had expired this year, due to the confusion on the Priority Date vs. Filing Date. The patent is still in effect, and is set to expire March of 2020.
As of March 7th of next year, the SIFT patent will expire in the U.S.
U.S. patents are valid for 20 years from the earliest filing date, but can be extended to 21 years if a Priority Date is used, and SIFT (US6711293B1) was filed (with priority) on 1999-03-08.
This means that usage of the SIFT algorithm will soon no longer requires a license for use.13