GPT-5.6 Sol vs GPT-5.6 Luna
OpenAI's GPT-5.6 Sol and OpenAI's GPT-5.6 Luna both target production language workloads, but they price and behave differently. Here is the side-by-side.
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The short answer
GPT-5.6 Luna is the cheaper option — roughly 17.8x less on a blended workload, and it suits high-volume work on a tight budget. GPT-5.6 Sol justifies its premium when you need frontier coding and long-horizon agents.
OpenAI • GPT-5.6
$4.00 / $20.00
/ 1M tokens (input / output)
OpenAI's flagship tier and the current state of the art on agentic coding benchmarks. Reasoning effort is tunable from none through max, and an `ultra` setting coordinates parallel subagents across workstreams. Sol reaches near-Fable-5 intelligence while spending markedly fewer output tokens, which is why its cost per finished task lands well below its sticker price.
OpenAI • GPT-5.6
$0.20 / $1.20
/ 1M tokens (input / output)
After an 80% price cut in July 2026, Luna became the value outlier among frontier-family models: it outperforms the previous generation's top-end Opus tier on coding evals while costing about a fiftieth of Fable 5 per input token. This is the model to route bulk traffic through in a tiered architecture.
Input price
GPT-5.6 Luna is 95% cheaper than GPT-5.6 Sol on input tokens.
Output price
GPT-5.6 Luna is 94% cheaper than GPT-5.6 Sol on output tokens — usually the side that dominates the bill.
Monthly cost at three workload sizes
Standard (non-batch, non-cached) rates. Reasoning models will exceed these figures because thinking tokens bill as output.
| Workload | GPT-5.6 Sol | GPT-5.6 Luna | Difference |
|---|---|---|---|
| Light — 1M in / 200K out | $8 | $0 | $8 |
| Moderate — 10M in / 2M out | $80 | $4 | $76 |
| Heavy — 100M in / 20M out | $800 | $44 | $756 |
Specification comparison
| Attribute | GPT-5.6 Sol | GPT-5.6 Luna |
|---|---|---|
| Input (/ 1M tokens) | $4.00 | $0.20 |
| Output (/ 1M tokens) | $20.00 | $1.20 |
| Cached input | $0.40 | $0.02 |
| Context window | 1,048,576 tokens | 1,048,576 tokens |
| Max output | 128,000 tokens | 128,000 tokens |
| Native reasoning | Yes | Yes |
| Knowledge cutoff | 2026-02 | 2026-02 |
| Relative latency | high | low |
| Open weights | No | No |
| API model ID | gpt-5.6-sol | gpt-5.6-luna |
| Status | stable | stable |
GPT-5.6 Sol: Promotional pricing (down from $5/$30) held at least through 2026-11-21. Prompts above 272K input tokens bill at higher rates; 'fast' processing is 2x.
GPT-5.6 Luna: Cut 80% from the $1/$6 launch price on 2026-07-30.
Choose GPT-5.6 Sol if…
- Long-running autonomous coding agents
- Large-scale refactors and migrations
- Agentic browsing and computer use
- Scientific and financial analysis
Choose GPT-5.6 Luna if…
- Classification and content moderation
- High-frequency agent subtasks
- Bulk summarization
- Cost-sensitive chat features
Frequently asked
Is GPT-5.6 Sol or GPT-5.6 Luna cheaper?
GPT-5.6 Luna is cheaper. On a blended 3:1 input-to-output workload it costs about 17.8x less than GPT-5.6 Sol.
Which has the larger context window, GPT-5.6 Sol or GPT-5.6 Luna?
Both accept up to 1.05M tokens, so context is not a differentiator here.
Should I use GPT-5.6 Sol or GPT-5.6 Luna?
Pick GPT-5.6 Sol for frontier coding and long-horizon agents. Pick GPT-5.6 Luna for high-volume work on a tight budget. If cost dominates the decision, GPT-5.6 Luna wins; if you need the capability ceiling, benchmark both on your own evals before committing.