GPT-5.6 system card details three model tiers

GPT-5.6 Sol costs $5/$30 per million tokens, matching GPT-5.5 pricing, and adds an Ultra thinking mode that spawns sub-agents. OpenAI calls it a "step function better" than GPT-5.5. Terra and Luna offer cheaper alternatives at $2.5/$15 and $1/$6 per million tokens respectively.