While the original BioShock was heavily scripted, Infinite will be a different experience every time you play.
One example is how NPCs, both friend and foe, can improvise depending on your actions. In one scene you walk through a shop selling souvenirs for the floating city of Columbia. If you take a certain path, Elizabeth - your AI-controlled partner - will pick up items and investigate, such as trying on hats. Take another path and she'll do something different.
Then there are the enemies. How they behave in combat depends entirely on how you behave. They're smart enough to adjust their tactics in real time depending on what kind of weapons you're using. Some won't even attack you at all, choosing not to get involved.
This is all thanks to an AI system that splits NPCs into three different camps: alphas, betas and gammas. Alphas are, essentially, bosses. Betas are reminiscent of Rapture's Splicers and will attack aggressively on sight.
Gammas, on the other hand, have their own lives to get on with, and may or may not get involved in any fights you start. It's a brilliantly clever and sophisticated system that should make Infinite feel much more dynamic and unpredictable than BioShock's effective, but scripted, ghost train.
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