The only safe and legal way to play the full, updated version of the game is through official channels:
: A core feature of Garry's Mod is the ability to download millions of community-made mods from the Steam Workshop. Pirated versions are locked out of 99% of this content. Garry’s Mod Free Download (Incl. Auto Updater)
: You generally cannot join official or popular community servers with a cracked version. The only safe and legal way to play
Downloading the game from third-party sites claiming to include "auto-updaters" or "full free versions" carries significant risks: Garry’s Mod Free Download (Incl. Auto Updater)