AlphaStar: Mastering the Real-Time Strategy Game StarCraft II

The numbers you cite are close enough that your estimations are good to work with (12 seconds to build, closer to 60 minerals at full efficiency but down to 40 for probes #17-24, etc)

The extra workers aspect was the most interesting decision-based adjustment AlphaStar made on conventional pro level wisdom of "standard" play. It has a couple of factors in play, that I trust the AI factored in and more and tested over several games for its long-term benefit to winning a game:

- every 8 probes you build requires a pylon as well. total cost of 500 minerals

- workers are safer in the main than in an unoccupied natural (long distance mining) to harassment and pressure

- when your expansion completes, having 4 workers vs 8 workers vs 16 workers potentially has huge impact to the immediate spike in income

- what you mention -- the prebuilt workers will dampen the impact of most worker harassment to purely the resource cost of the lost workers.

My guess was that well executed harassment by an opponent in practice games put AlphaStar in very limited situations with a crippled economy that it couldn't fight its way out of, so this was a catch-all harassment "counter" -- it's ok if you kill a few probes, at least it won't throw off my economy completely and I can still continue my overall gameplan.

After that I think the next most important aspect was planning ahead for a bigger income spike when their expansion was done without waiting to build out another 16 workers after the nexus was ready.

They mentioned that they retrained after the camera change and it was equivalent to the AIs that beat Mana 5-0 by their metrics.

Perfect information is a bit of a stretch. There was still fog of war. The AI just played as if the portion of the map visible and actionable at any point in time was the whole map. They retrained with a restriction to a given locus of attention that can change, akin to a screen the player is looking at and acting on.

APM is a really really misleading metric to use here. Most starcraft pros spam keys to keep themselves loose and ready when the time comes. Even at the start of a game, you'd often see players with 500 apm warming up the fingers.

Here, there is the laughable graph of the computer apm over time. The key points here is that when there were the mass battles that won the game, the apm spiked to >1000. And if you look closely in slow motion, there was perfect split targeting. A human player wouldn't be able to perfectly select the exact number of stalkers to hit the enemy without wasting a surplus shot. They can, but not when it's mass stalkers. This efficiency is just beyond humans. The APM here indicates much more effective use of an action than a typical human.

This is super impressive as an achievement, but this is clearly not a smarter ai, but moreso an ai like the video a while ago where zerglings could perfectly micro against siege tanks to avoid splash damage. It is clearly better than humans in certain ways, but not smarter.

While the "skill cap" on blink stalkers is extremely high, there are many hard counters that can stop even perfect blink micro. MaNa won because he went for one these. Immortals are the perfect hard counter to stalkers because

- cost-for-cost, they are more efficient in a faceoff (resources)

- immortals are space-efficient dps (damage per second) in a battle. In a given battle, an army of 4 immortals is far more likely to all be in range of an enemy and doing damage than an army of 8 stalkers bumping against each other trying to get to the priority target

- immortal shots do not have projectiles, but are instant. No matter how perfect your stalker control, once an immortal targets a stalker, it is guaranteed to take 30+% of its hitpoints in damage.

The last point is very important. Once MaNa had 3+ immortals, even with perfect blink micro, a little bit of target fire and timing micro on MaNa's part allowed him to slaughter the stalker army one stalker per volley, while it takes them longer to clean up the immortals (especially with shield battery support).

Another thing glossed over in this discussion -- AlphaStar did more than classic blink micro. It did a very technical maneuver (the casters briefly allude to it) of triggering the barrier on one immortal with a single laser, then focusing all fire on an immortal whose barrier was already down from a previous iteration of this tactic, and then walking away until the barrier has worn off (while blink-microing weakened stalkers). Repeat. This is a detail of increasing the efficiency of trading stalkers with immortals that humans don't often even think about, let alone execute (because good blink control is often more impactful). That AlphaStar came up with this shows that it's not just about perfect execution of micro, but also perfect understanding of micro.