If you missed the B&H one-day sale, BuyDig is now featuring the Sigma Art 18-35mm f/1.8 DC HSM for Canon also for $549.00. This is the lowest price seen yet for this stellar lens.
Please note this is a DC lens for crop sensor bodies only. This deal is today only or until sold out.
Amazon (through Beach Camera) has it for $549 as well. If you have one of the Prime credit cards then also a potential 5% back. Also, obviously, Beach Camera also has it for $549.