OpenAI GPT-5.6 arrives as three models: Sol, Terra and Luna

OpenAI's GPT-5.6 generation shipped as a family of three named variants rather than one model: Sol, Terra and Luna.

The naming shift

Splitting a generation into named siblings is now standard practice across the industry — Anthropic has Opus, Sonnet and Fable; Google has Pro, Flash and Flash-Lite. The names typically encode a capability-versus-cost trade-off rather than three different underlying systems.

Of the three, GPT-5.6 Sol is the variant that shows up most often in comparisons: Moonshot AI cited Sol (alongside Claude Fable 5) as one of the two models its own Kimi K3 still trails on overall performance.

The review that delayed it

Reporting on the July release cycle says OpenAI opened access to GPT-5.6 after a twelve-day government review. Take that specific figure as reported rather than confirmed — but the direction of travel is real and worth watching, because it is the same thread as the export-control episode that briefly pulled Claude Fable 5 out of general availability.

Pre-release government review is a live constraint on frontier releases now, not a hypothetical. For anyone building on these APIs outside the US, that is the risk to plan around: not that a model gets worse, but that availability changes without notice.

Dates, honestly

Trackers list GPT-5.6 Sol, Terra and Luna on 26 June 2026; a second source dates the Sol and Luna entries to 9 July 2026 — most likely the difference between an initial release and a wider availability step. We have not been able to reconcile the two from public sources, so we are reporting both.