GPT-5.6 system card details new models Sol, Terra, Luna

OpenAI's system card describes three GPT-5.6 models: Sol (flagship, $5/$30), Terra (competitive to GPT-5.5 at half cost), and Luna (most cost-efficient at $1/$6). New thinking settings include Max and Ultra, which allows sub-agents. Sol will be available on Cerebras at 750 TPS but with limited capacity initially.