GPT-5.6 introduces Sol, Terra, and Luna as explicit model tiers

A three-tier family

OpenAI released the GPT-5.6 family on July 9, 2026, introducing Sol, Terra, and Luna. Its documentation identifies Sol as the flagship tier and notes that the unsuffixed GPT-5.6 alias routes to Sol.

For developers, precise model identifiers became especially useful when comparing capability, latency, and cost across the family.

An alias is an operational dependency

An application may use a convenient short name while its billing or evaluation record expects a particular tier. Keeping that mapping explicit helps explain changes in behavior and prevents a configuration typo from silently selecting a different class of model.

A model-routing rule should also describe the task conditions that justify each tier. Otherwise, the system can become difficult to audit as exceptions accumulate.

Record the route with the result

Store the requested model, resolved tier where available, relevant settings, and task outcome in the evaluation record. Compare total cost per accepted deliverable rather than token price alone. Recheck the route when documentation or aliases change. Clear naming does not eliminate model-selection work, but it gives the team a better vocabulary for describing the tradeoffs it is making.