Starcraft AI blog

The drop opener dynamic vs. PurpleWave is trickier than it looks.

On first glance, yes, PurpleWave sees the cannons and reacts appropriately. There's a lot of nonsense you can do (and bots do do) behind cannons (Carrier rush, DT rush, fast expansion, 4-Gate Goon, 4-gate proxy mass slowlot), and PurpleWave's reaction is sound against them all (expansion into Observer + Reaver).

PurpleWave also generally comes out of the drop itself in good shape. It could do a better job of saving probes but it still tends to wind up ahead economically.

One little advantage is adding noise to PurpleWave's learning data. Because that cannon reaction can come out of any opener, and PurpleWave's learning doesn't understand that a deviation happened, you make it harder for PurpleWave to learn what builds work against your bot as a whole. I think this effect is fairly minor.

A nastier bit about the drop build is that it forced PurpleWave into a Shuttle+Reaver composition, which was new in AIIDE and still shaky. So shaky that Locutus could frequently overcome its build order disadvantage by virtue of PurpleWave throwing its Reavers.

The other nasty bit -- and the more significant one, I think -- is that it forces PurpleWave to throw out its well-oiled opening book for PvP. PurpleWave thrives on gaining early-game advantages by detecting what you're doing and reacting correctly. This goes down to the resolution of "do I even bother making Zealots before my first Dragoon?" -- it really tries to get every edge and cut every corner it can. But opening cannons means it's settling for the moderate-but-not-lethal advantage of having a faster expansion and better (in theory, but frankly worse than pure Dragoon in execution) tech. And the damage dealt by the drop comes close to evening that advantage back out.

So mainly it's the combination of guaranteed early game survival vs. PurpleWave + forcing out PurpleWave's mediocre Shuttles that let the drop opening make for a fair fight against PurpleWave.