GPT-5.6 ships as a tiered family rather than a single model. Sol sits at the top, tuned specifically for biology, chemistry, and cybersecurity — a narrower capability profile than a general frontier model but deliberately deeper in those domains. Luna is the lightweight, cheapest option. Terra lands in the middle and is the one most developers will care about: OpenAI claims it matches GPT-5.5 performance at roughly half the cost, which if it holds up in practice is a meaningful shift for teams running high-volume inference. The rollout required a Department of Commerce sign-off after additional government testing — a procedural step that OpenAI had already navigated for the 20 partners who received preview access in late June. The public launch completing that arc on July 9 is the practical end of the preview period, not a surprise release.