Wow its been a long time since an update also this does not require Source SDK 2007
To run GuestSandbox, please use the "Source SDK Base 2013 Multiplayer." Please note that "Multiplayer" is indeed the correct option. We have incorporated a range of Half-Life 2 beta weapons into the mod and have also introduced Multiplayer & Singleplayer support. Additionally, we invite you to join our new Discord server, where you can connect with the developers and stay updated on further developments.
Discord :
Discord.gg
TYSM for downloading