Last week was the highlight of the dota 2 competitive year: It was the week of The International, Valve’s biggest tournament. On Saturday, Team Liquid walked away with over $10 million after beating Newbee 3-0 in the grand final.
At this point, one of the requirements to be a good one is dota 2 player is that you have to be a living, breathing human being. The game features some basic computerized bots to practice against, but any seasoned player of the game should have no trouble overcoming these bots, even on their hardest “Unfair” difficulty setting (although the Unfair Viper bot is a legendary jerk who totally sorry to play against). Last Friday, however, we got a hint of a new, all in all, more threatening kind of computerized player: an AI-powered bot built by Elon Musk’s OpenAI. The OpenAI bot took on some professional players and crushed them.
The OpenAI bot can’t play the full game from dota 2. It can only play one hero, Shadow Fiend, of the game’s 113 playable characters (with two more later this year); it can only play against shadow devil; and instead of playing in five-on-five matches, it plays a very limited subset of the game: one-on-one solo matches.
These are not random choices; 1v1 solo mid Shadow Fiend mirror matches, where two people both play Shadow Fiend against each other, are a classic showcase of individual player skills. Shadow Fiend is played this way for a few reasons. First, he has three skill shot magic attacks (near, medium, and far Shadow Razes) that place a particular emphasis on positioning and judgment to successfully land (or dodge) the attack.
Second, while his normal attack damage starts very low, he has a very powerful steroid ability called Necromastery. Every time he successfully lands the deadly blow on a creep (automated drone units that spawn every 30 seconds and fight each other mindlessly), he captures that creep’s soul and takes two points of bonus damage. This means that more than most other heroes in the game, Shadow Fiend rewards especially accurate last hits (the dota 2 terminology for a fatal blow).
The OpenAI bot doesn’t know how to play dota 2. But during hundreds of in-game hours of playing 1v1 solo mid Shadow Fiend games against itself in Microsoft’s Azure cloud, the AI started learning how to win the game. Early iterations of the bot AI would simply remain in their base, wander aimlessly around the map and end up being killed in stupid ways. As we would expect from a bot, the AI is very strong to finally strike; it can judge exactly when to time its attacks to make the deadly blows. Likewise, it is very good at accurately judging the range of its Shadow Raze spells.
But the bot went further and discovered other techniques known to human players. For example, the Shadow Raze spell has a short wind-up before the spell is actually cast. If a “stop” command is given during this winding, the spell is canceled. This fake casting is useful because opponents will see the wind-up and try to dodge the incoming spell; a well-timed fake cast can force the opponent to move to a less favorable position or miss a final hit, without consuming mana or putting the spell on cooldown. The AI can also manipulate the creep position by selectively drawing their aggression.
After about two weeks of training, the OpenAI bot was able to consistently de dota 2 pluses. Over the course of last week, it pitted against big names on the scene such as Artour “Arteezy” Babaev and Sumail “Suma1L” Hassan (both of the North American team Evil Geniuses), and former pros such as William “Blitz” Lee. All of these players are known for their mid lane play (where one-on-one matchups are the norm); none of them took a game from the AI. On stage, we saw the bot take on Danil “Dendi” Ishutin, arguably the most beloved of them all dota 2 players and another strong middle player. The bot crushed him relentlessly 2-0.
After beating the pros, the bot was thrown open to KeyArena participants. In-game cosmetics were offered to the first 50 people who could beat the bot. The bot has indeed fallen, with all 50 cosmetics are wonusually using cheap techniques to distract the enemy creeps or buy unusual items. This takes advantage of a weakness of the AI; it is far less good at handling situations it has never seen before than a human would be.
The OpenAI team says play dota 2, even in this limited way, is considerably more complex than playing a game such as chess or Go. Not only is the range of possible actions wider, but dota 2 has hidden information; for example, players can stand out from view so that the bot doesn’t know where an attack might come from. The next goal of OpenAI is to develop bots that can play full five-on-five matches, collaborate and interact with each other to play as a real team.
That’s a vastly bigger undertaking, of course, but if they can pull it off, humanity’s domination is… dota 2 is going to end clearly: Skynet is going to beat us all.
List image by Valve