# GPT-5.6 Luna

OpenAI, released 2026-06-26

**Verdict: conditional.** GPT-5.6 Luna is OpenAI's previous-generation budget model at $0.20 input and $1.20 output per 1M tokens short context, generally available through the API and Codex. Its successor GPT-6 Luna, released 22 September 2026, lists at $0.10/$0.50, so Luna is no longer the low-cost default for new OpenAI work. It remains conditional because benchmarks are vendor-reported and it lacks activation classifiers; OpenAI lists no deprecation, so existing pipelines need not migrate yet. Last verified 2026-09-27.

## Pricing

- Input: $0.20 / 1M tokens
- Output: $1.20 / 1M tokens
- Context: Short $0.20/$1.20 · long $0.40/$1.80 per 1M

## Strengths

- Best capability-per-dollar within the GPT-5.6 family: TerminalBench 2.1 at 82.5% is only 0.9 points behind GPT-5.5 (83.4%) at $0.20 input / $1.20 output per 1M, against Sol's $4 / $20.
- Speed and throughput: positioned as the fastest GPT-5.6 model, optimized for latency-sensitive products, agent swarms, customer support, and real-time classification pipelines.
- Routine automation and extraction: classification, summarization, formatting, routing, draft generation, and background automation where cost-per-request and throughput dominate over raw reasoning depth.
- Model-routing architectures: the bottom tier of a Sol > Terra > Luna escalation ladder. Use Luna by default, escalate to Terra or Sol when Luna's eval score drops below threshold on a specific task.
- Long-context jobs budgeted off the headline rate: past short context Luna bills $0.40 input and $1.80 output per 1M tokens.
- CTF score of 85.19% is the lowest in the family: solid but not dominant. For security-critical workflows, Terra or Sol are the appropriate tier.
- Lacks the safety depth of Sol and Terra: no activation classifiers on Luna (per system card). For regulated cyber and bio workflows, use Terra or Sol with full monitoring stack.
- Buying purely on lowest list price: DeepSeek's V4.1-Flash lists $0.15 input / $0.60 output per 1M off-peak, below Luna on both, though its weekday peak input rate ($0.30) is higher.
- New high-volume deployments chosen on price: its successor GPT-6 Luna, released 22 September 2026, lists at $0.10 input / $0.50 output per 1M short context against GPT-5.6 Luna's $0.20 / $1.20

## Benchmarks

- TerminalBench 2.1: 82.5% (https://openai.com/index/previewing-gpt-5-6-sol/)
- Internal CTF (capture-the-flag): 85.19% (https://venturebeat.com/technology/openai-unveils-gpt-5-6-sol-terra-and-luna-models-but-only-accessible-to-limited-preview-partners-for-now-per-us-gov)

## Sources

- [OpenAI: GPT-5.6 Preview System Card](https://deploymentsafety.openai.com/gpt-5-6-preview)
- [OpenAI — Previewing GPT-5.6 Sol](https://openai.com/index/previewing-gpt-5-6-sol/)
- [OpenAI Docs: API changelog (Decisions API beta, October 6, 2026)](https://developers.openai.com/api/docs/changelog)
- [OpenAI API pricing](https://developers.openai.com/api/docs/pricing)
- [Kingy AI: OpenAI GPT-5.6 Sol Benchmarks and Specs](https://kingy.ai/news/openai-gpt-5-6-sol-benchmarks-specs-pricing-safety-evals/)
- [VentureBeat: GPT-5.6 Sol, Terra and Luna models](https://venturebeat.com/technology/openai-unveils-gpt-5-6-sol-terra-and-luna-models-but-only-accessible-to-limited-preview-partners-for-now-per-us-gov)
- [Lushbinary: GPT-5.6 Sol Benchmarks Deep Dive](https://lushbinary.com/blog/gpt-5-6-sol-benchmarks-terminalbench-agentic-deep-dive/)
- [OpenAI API docs: Deprecations](https://developers.openai.com/api/docs/deprecations)

Canonical: https://neomanex.com/models/gpt-5-6-luna