OpenAI split one model into three price tiers - and put its coding agent to work inside them.
GPT-5.6 isn't one model, it's a generation. The number 5.6 only shows when it was born, not how strong it is - the strength comes from the name next to it. This is a change in approach: before, version and power moved together (GPT-4, then GPT-5), now the generation and the capability level move on separate rhythms, so that Sol, Terra and Luna can each update on their own, without waiting for the next big version of the whole family.
Sol is the top - the flagship model, the most expensive to use and the only one with access to the full "maximum mode" of thinking, a mode for the hardest multi-step tasks. Per unit of text you pay several times more through it than through the cheapest of the three, which says enough about the gap in ambition between them.
Between the two stands Terra - balanced for everyday work, made to do almost the same as the company's previous flagship, but at half the price. This is probably the model most products will actually use, because the trade-off pays off and the difference rarely shows.
Luna is the base - fastest, cheapest, for tasks that don't need deep reasoning, just a quick, good-enough answer. The volume runs through it: chatbots, small automations, everything that happens thousands of times a day and can't pay flagship price every time.
Codex is a different beast. It sits outside the Sol/Terra/Luna trio - OpenAI's separate coding agent, a system that goes into a project on its own, runs commands, fixes bugs and proposes code for review, instead of just answering a question. Since early July it's built into the ChatGPT app itself and runs on GPT-5.6 underneath. Over five million people use it weekly - a number that shows writing code is stopping being something you do alone in front of a screen. It's becoming something you hand off.
Let's not dance around it
This split is something I've been doing at the agency for years: not every task deserves the most expensive person in the room. OpenAI just said out loud what the industry was already doing quietly. Sol, Terra and Luna aren't three different products under one label. They're one family with different characters - one is for the hardest problem, the middle one does most of the work, the small one runs fast and doesn't ask questions.
The real news for me isn't the trio of models. It's Codex inside them - a coding agent built into a model that decides on its own how much "to think" before writing a line of code. That's the direction everything I do here is heading. I no longer ask which model is "the best." I ask which one is good enough for this task, at this price, right now.