Blog Post: How to Play the GTA Trilogy Definitive Edition for Free
If you already owned the original versions of these games on the (PC) before the Definitive Edition launched, Rockstar previously offered the classic versions for free as a "thank you" for the launch issues. While this specific promotion has ended, always check your library if you are a long-time Rockstar social club member. Blog Post: How to Play the GTA Trilogy
While not permanently free, the trilogy frequently appears on various gaming subscription services: Blog Post: How to Play the GTA Trilogy