GPT-5.6 Luna
OpenAI released 2026-07-09 proprietary
Nothing is both better and cheaper.
Under a balanced workload, no other model in the catalogue scores higher and costs less. This model is on the value frontier.
The same model via batch is 50% cheaper ($0.225/M) — same weights, different latency.
Our take
editorial — not a measurementThe cheap end of the 5.6 family at $0.20/$1.20 with the full 1.05M context window, which is an unusually good context-per-dollar ratio for a proprietary model. It is also the model OpenAI gives away — ChatGPT Free offers unlimited Luna chat — which tells you where it sits on the capability curve. Treat it as a high-volume utility model: cheap, long-context, not frontier. The long-context tier doubles it to $0.40/$1.80, still cheap.
Strengths
- $0.20/$1.20 with a 1.05M context window
- Cached input at $0.02
- Cheapest route to a very long proprietary context
- 50% batch discount
Weaknesses
- Well below frontier capability — it is the free-tier ChatGPT model
- Long-context tier doubles input price
- Open-weight models undercut it on raw token price
Reach for it when
- High-volume summarisation over long documents
- Cheap long-context retrieval
- Free-tier-equivalent workloads at API scale
Avoid it if
- The task needs frontier reasoning
- You can host open weights
Sources: developers.openai.comchatgpt.com
Every price dimension
| Input | $0.200/M |
|---|---|
| Output | $1.20/M |
| Cached input | $0.020/M |
| Cache write | $0.250/M |
| Web search | $0.01/call |
| Batch discount | 50% |
Past 272,000 tokens the price changes. Input goes to $0.400/M (2×) and output to $1.80/M. The headline rate does not apply to a long-context workload.
Independent scores
| Intelligence | 52.3 |
|---|---|
| Coding | 71.4 |
| Agentic | 46.9 |
| LMArena Elo | 1428.5xhigh |
Sources are listed separately rather than averaged. Across the 62 models both have scored they correlate at r = 0.806 — close agreement overall, but four models rank very differently between them, and a blended score would hide exactly those.
Capability
| Context window | 1.1M |
|---|---|
| Max output | 128K |
| Input modes | file, image, text |
| Tool use | yes |
| Reasoning | optional |
| Knowledge cutoff | 2026-02-16 |
| Open weights | no |
Provenance
| Price source | openrouter.ai |
|---|---|
| Fetched | 2026-08-24 |
| Quality data | verified |
| Cross-checked | vendor page |
GPT-5.6 Luna is a fast, cost-efficient model in OpenAI's GPT-5.6 series. It is suited for high-volume, latency-sensitive tasks such as chat, classification, and lightweight agentic workflows, providing capable reasoning for...