Alien Swarm comes with bot AI which normally appear in Offline Practise mode. They can also be included in multiplayer games with a few simple console commands. This allow four marines in a game with less than four players, and to create a "safer" environment to experiment with new tactics or weapons.

The following quirks and limitations apply when playing with bots in multiplayer.

• Bots can only be added or removed at the lobby screen.
  
• Bots "belong" to the player that created them. Only the creator player can take manual control of a bot by using the F1 to F4 keys. However, the bots will listen to general movement commands such as "stop" or "go" from all players.
  
• Bots don't switch their weapons until ammo runs out (except for medics with the medical gun)
  
• Medic bots with the medical gun often can't decide whether to heal or to shoot, causing it to endless switch weapons.
  
• Bots do not know how to deal with mortar bug barrages.
  
• Bots do not know how to use alt-fire (maybe except for minigun spooling?) and most off-hand items.
  
• Scoring is glitched if you end the level while controlling a different character than at the beginning.

To open the console, press the ~ key ("tilde") when you are in the game lobby.

To add bots, use the following console command:
{marine} is a number from 0 - 7 as per following:

• 0 Sarge
  
• 1 Wildcat
  
• 2 Faith
  
• 3 Crash
  
• 4 Jaeger
  
• 5 Wolfe
  
• 6 Bastille
  
• 7 Vegas

{slot} is either a number from 0 to 3 that corresponds to a slot in the list of players, or -1 for the next available empty slot.

To remove bots, use the following console command:

Search the web for "https://www.google.com/?q=Alien+Swarm+foxbot.cfg" for an example of a .cfg file that nicely binds the commands to keys for quickly adding and removing bots.