GPT-5.6 Luna

At a glance

Reached general availability on July 9, 2026. GPT-5.6 ships as three tiers - Sol, Terra, and Luna - and Luna is the one built for high-volume, latency-sensitive work: chat, classification, and lightweight agent flows.

Three weeks after launch OpenAI cut Luna's API price by 80% (to $0.20 per million input tokens and $1.20 per million output), which is why it lands in the 1-credit tier on Magnus - cheaper than GPT-4o mini, newer than everything else in the lineup.

Benchmarks

• GPQA (graduate-level science questions): 64.5%.
• The benchmark gap to its big siblings is far narrower than the 25x price gap - the reason it punches so far above its credit cost.

Best at on Magnus

Everything you would use a small model for, done better: daily chat, summaries, drafting, and chatty secondary agents. If you run OpenAI and are not sure which model to pick, start here.

• Luna at 1 credit is the cheapest way to try a 2026-generation model on the All-inclusive plan.