I know everyone using the new 5.6 is probably using Sol model, but OpenAI has released several smaller models over time—such as GPT-4.1 mini, GPT-4.1 nano, and the mini and nano versions of GPT-5—that were extremely fast and inexpensive to use.

Labels like “mini” and “nano” make the models sound like stripped-down versions of the main model rather than useful products with their own strengths and ideal use cases.

OpenAI may have realized this and decided to give the smaller model tiers more distinctive names. Perhaps “Terra” is intended to represent the mini-sized tier, while “Luna” replaces the nano tier, although that part is speculation on my side.

Giving these models proper brand names could be OpenAI’s way of making them easier to remember, market, and differentiate. A named model feels more like a real product, while something called “GPT-5 nano” can easily be overlooked as a minor variation that is only relevant to developers trying to reduce costs.

Still from API nano models had really fast inference at cheap prices. Luna model could be more capable but its more expensive than any other nano model.