GPT-5.6 Luna

GPT-5.6 Luna is the fast, low-cost tier of OpenAI’s GPT-5.6 family, which began a limited government-vetted preview in late June 2026 before opening to the wider public on July 9, 2026 once the US Commerce Department’s Center for AI Standards and Innovation cleared broader access. Luna is built for summarization, drafting, and high-volume automation where speed and cost matter more than maximum reasoning depth, and it shares the family’s 1.05 million token context window with support for up to 128,000 output tokens. At $1 per million input tokens and $6 per million output tokens, it undercuts the mid-tier Terra model by a wide margin while still handling everyday chat and lightweight coding tasks. OpenAI pitched the three-tier Sol, Terra, Luna structure as a way for developers to trade off cost against capability without switching model families, following the same pattern it used with the GPT-5 mini and nano tiers.