Subpixel hinting mode can be chosen by setting the right value in your environment, for example /etc/environment or ~/.pam_environment

Available settings:

      FT2_SUBPIXEL_HINTING=0  # Classic mode (default in 2.6)
      FT2_SUBPIXEL_HINTING=1  # Infinality mode
      FT2_SUBPIXEL_HINTING=2  # Minimal mode (default in 2.7)