GPT-5.6 Sol, Terra, and Luna
Create an agent or open an existing agent in the builder, then follow the steps below. Model and feature availability may depend on your plan.
What it does
OpenAI's GPT-5.6 family arrived in three variants, each selectable per agent.
Before this
An addition to the selector. GPT-5.5 had been OpenAI's newest since April; 5.6 replaces it with three variants instead of one, which is the actual change — the choice of depth moved from inside the model to the model list.
Why it matters
Three points on the speed-versus-depth curve from one provider, so you can tune cost per agent without changing how your prompts behave.
The specs
OpenAI shipped GPT-5.6 as three separately selectable models rather than one model with a size dial, so you pick the point on the speed-versus-depth curve per agent.
- Shared specs
- All three take 1,050,000 tokens in and produce up to 128,000 out, read text and images, and support Actions.
- Sol and Terra
- Carry the 'smartest' tag — the two to reach for on hard reasoning.
- Luna
- The lighter sibling for everyday work.
- Reasoning
- Fast ($$), Smart ($$$), or Smartest ($$$$) on all three.
- Plans
- Gold and Pro.
Because the three share a context window and prompt behaviour, moving an agent between them is a one-dropdown change — you can tune cost after launch without re-testing your prompt.