GPT-5.6 Luna

GPT-5.6 Luna is OpenAI's fast, affordable GPT-5.6 tier, not the frontier Sol row. Rechecked 2026-08-18: developers.openai.com/api/docs/models still says start with GPT-5.6 Sol, then lists Luna as the cheap/fast sibling. The first-party GPT-5.6 Luna card prints 128,000 context, 128,000 max output, and $1.00 input / $6.00 output per 1M tokens (cached input $0.10). Knowledge cutoff on that card is February 16, 2026. Reasoning effort tops at high. Do not invent a Luna-only max / ultra crown from the Sol page.

Compare GPT-5.6 Sol if you wanted the live frontier, GPT-5.6 Terra if you wanted the 400k daily driver, and GPT-4o mini if you wanted the leftover cheap omni snapshot.

Key Features

• Cheap/fast 5.6 tier: Docs place Luna under Terra and Sol.
• Printed context: 128k input / 128k output on the Luna card we opened.
• Printed dollar row: $1.00 / $6.00 per 1M, cached input $0.10.
• Effort up to high: Recheck the Luna card. Do not paste Sol max / ultra or Terra xhigh onto Luna.

Use Cases

• People who wanted a live cheap GPT-5.6 row instead of leftover GPT-4o mini.
• People comparing Luna $1/$6 vs Terra $2.50/$15 vs Sol $5/$30.
• People who only had a Sol page and needed the affordable sibling.

Limitation: We did not re-run Sol benches on Luna or invent a 2026 speed crown.

Pricing

GPT-5.6 Luna card on 2026-08-18.

If a leftover blog only mentions Sol, treat Luna as the printed cheap/fast row.

Getting Started

1. Open the GPT-5.6 Luna card and note $1 / $6 and 128k context.
2. Recheck GPT-5.6 Terra if you wanted the 400k daily driver.
3. Recheck GPT-5.6 Sol if you wanted the live frontier.
4. Do not paste Sol max / ultra onto Luna.

Frequently Asked Questions

Is Luna the start-here model?

No. The models index still starts at GPT-5.6 Sol. Luna is the cheap/fast sibling.

Same as GPT-4o mini?

No. GPT-4o mini is a leftover cheap omni snapshot at $0.15 / $0.60. Luna is the live 5.6 cheap/fast row at $1 / $6.

Same as Terra?

No. Terra is the 400k daily driver at $2.50 / $15. Luna is smaller and cheaper.

Alternatives

• GPT-5.6 Sol: Live OpenAI frontier.
• GPT-5.6 Terra: Balanced 400k daily driver.
• GPT-4o mini: Leftover cheap omni snapshot.

Tips

1. Quote $1 / $6 and 128k from the Luna card, not the Sol page.
2. Call Luna cheap/fast, not the frontier.
3. Recheck Terra if you needed the 400k window.

Conclusion

GPT-5.6 Luna is the live cheap/fast GPT-5.6 tier at $1 / $6 with a 128k context, not the Sol frontier. Start at the Luna card, then decide whether GPT-5.6 Terra or GPT-5.6 Sol already covers the path you need.