Click on and look for "Download offline backup game installers." Download the setup_terraria_v1.4.4.9 file.
Note: tModLoader for GOG is currently in a transition phase. The "Alpha" version is now the primary branch for GOG users to access newer mods. terraria 1449 gog install
You can install the game using either the GOG GALAXY client or a standalone offline installer. Launch GOG GALAXY and log in to your account. Navigate to the "Owned Games" tab on the left sidebar. Search for Terraria and click the Install button. Click on and look for "Download offline backup