Qt

Qt is a cross-platform application and UI framework - some tools available for no charge from Valve utilize Qt.

Valve ships a modified version of Qt, primarily to allow interoperation with the rest of Source2:

• Valve-Modified Qt 5.15.2 for Win64 (Source 2 Workshop Tools since March 2021, Dark Mode is available on this version.)
  • Valve-Modified Qt 5.15.2 for Win64 - May 2023 Update (compatible with previous 5.15.2 binaries)
• Valve-Modified Qt 4.8.3 for Win64 (Source 2 Workshop Tools released before 2021)

To confirm the version of Qt being used, you can select "About Qt" from the Help menu in the Asset Browser or other tool windows.

List of GoldSrc, Source and Source 2 games and software/tools that uses Qt:

• Aperture Desk Job
• Black Mesa
• Dota 2
• Destinations
• Half-Life 2: Remastered
• Half-Life: Alyx
• Source Filmmaker
• SteamVR Home
• The Lab