it Looks like Opening 29OCT, but not operational until end Dec 2018:
https://www.bloomberght.com/haberler...ihi-belli-oldu
Funda Ocak, General Director of State Airports Authority (DHMİ), called the meeting of aviation organizations, including the airlines, to move to Istanbul New Airport on 29 October.
In the article about the meeting, it is stated that after the opening of the new airport in Istanbul on 29 October with a ceremony, the "Big Bang" procedure, which is planned to be held on 30-31 October, will be carried out on 30-31 December 2018 and will be used for "testing the integrated terminal facilities of the process"..
(courtesy of Google Translate)