GPT-5.6 Luna

GPT-5.6 Luna is the version of OpenAI's model lineup that gets assigned by default to users who don't pay. Think of it like a restaurant: paying members get a more elaborately prepared course meal (GPT-5.6 Sol), while free customers get the standard menu item from the same kitchen — and that standard item is Luna.

Luna's price has recently dropped sharply. Both the cost of generating output and the cost of reading input fell 80% each, a move widely seen as OpenAI's response to cheap competing models from China closing the performance gap. Free users won't notice this directly, but for businesses pulling this model via the API, the bill shrinks noticeably.

The article reports that "OpenAI cut the input and output token prices of GPT-5.6 Luna by 80% each." One easy point of confusion: Luna isn't OpenAI's flagship model — it's the default model assigned to free and Go-tier users. The more advanced paid version goes by a separate name, GPT-5.6 Sol. The two shouldn't be mistaken for one another.