The promised M4 extension to Sabiha aiport (SAW), in Istanbul, is it open yet? or do we still have to drive to Pendik to get on it? https://www.metro.istanbul/YolcuHizmetleri/AgHaritalari (is out of date, the google maps are not supported any more)
The metro map on the official website still shows the section as being under construction - https://www.metro.istanbul/YolcuHizmetleri/AgHaritalari I was also able to find this (https://www.railtech.com/policy/2018/11/30/two-istanbul-airports-to-get-metro-link-in-2019/) which states the expected opening date is the 29th of October 2019 (published November 2018).
The extension is also shown as being built on Wikipedia (https://en.m.wikipedia.org/wiki/M4_(Istanbul_Metro)) and Open Street Map (https://www.openstreetmap.org/#map=13/40.8909/29.2826&layers=T) both of these being publicly available does mean that I wouldn't recommend considering them if they where the only sauce, but this does mean that they tend to be updated quickly - especially in large cities.
I'd therefore say the extension is not yet open, although with the caveat that I am not remotely familiar with the area. And this answer is based only on what I can find out online.