The New Istanbul Airport started operation since 29 October 2018, there are a few domestic flights for now.
Due to new airport there is no any subway goes to the New Istanbul Airport but bus services for this airport operated by HAVAIST bus company, number of the bus from the Istanbul Airport ( new airport ) to TAKSIM is IST-19. From Taksim go into the underground station and take the one-stop (F1) subway line down to Kabatas to take Tram(T1) to get to Sultanahmet Old City.
Private Istanbul Airport Transfer Service is available for New Istanbul Airport find more information below;
https://www.turkeytravelconsultant.com/tours/New-Istanbul-Airport-Arrival-Transfer
