According to the Athletic, the transfer includes an initial fee of £15.4 million, with a further £1.7 million in performance-related add-ons.
The move has not yet been completed, as personal terms between the player and the Turkish club are still being finalised.
Trossard, 31, has just one year remaining on his Arsenal contract, making the agreed fee a satisfactory return for the Premier League champions.
Since joining Arsenal from Brighton in 2023, the Belgian international has been a key contributor, helping the Gunners secure the league title.
He is currently on international duty with Belgium, who recently staged a dramatic comeback victory over Senegal to reach the next round.