What are the GPT-5.6 models?

They are three new versions from OpenAI: Sol (the most powerful), Terra (balanced between performance and efficiency), and Luna (designed for speed and low cost).

Why is its release limited?

Due to guidance from the US government based on security and cyber concerns, they are only available to companies pre-approved.

Is this approach permanent?

OpenAI considers this approach temporary and not part of its long-term plan, with potential expansion of access in the coming weeks.

OpenAI Launches GPT-5.6 Model in Three Versions with Limited Government-Guided Release | Wabl

OpenAI has announced the release of the new GPT-5.6 models in three versions-Sol, Terra, and Luna-but access is restricted based on a recommendation from the US government, in establishing a new approach toward regulating advanced models.

Wabl