When GPT-5.6 landed as three models instead of one, my first reaction was mild annoyance. Sol, Terra, Luna — great names, zero help when I'm staring at a config file deciding which string to paste into model. So I did the boring thing: I wired all three into the same app, ran a week of real traffic through them, watched the token meter, and wrote down what I learned. This is that write-up — the decision tree I wish someone had handed me on day one.
The 30-second version
Three tiers, same API shape, same features. The only thing that changes is depth vs. cost vs. latency. Official OpenAI list prices, per million tokens:
Tier
Model string
