GPT-5.6 Luna vs Claude Opus 5
OpenAI's GPT-5.6 Luna and Anthropic's Claude Opus 5 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 22.2x less on a blended workload, and it suits high-volume work on a tight budget. Claude Opus 5 justifies its premium when you need most teams' best claude starting point.
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.
Anthropic • Claude 5
$5.00 / $25.00
/ 1M tokens (input / output)
A step change over Opus 4.8 on deep reasoning and long-horizon agentic work, at half Fable 5's price and with the freshest knowledge cutoff in the Claude line. Anthropic's own guidance is that most teams should benchmark Opus 5 before paying for Fable 5.
Input price
Claude Opus 5 is 25.0x the price than GPT-5.6 Luna on input tokens.
Output price
Claude Opus 5 is 20.8x the price than GPT-5.6 Luna 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 Luna | Claude Opus 5 | Difference |
|---|---|---|---|
| Light — 1M in / 200K out | $0 | $10 | $10 |
| Moderate — 10M in / 2M out | $4 | $100 | $96 |
| Heavy — 100M in / 20M out | $44 | $1,000 | $956 |
Specification comparison
| Attribute | GPT-5.6 Luna | Claude Opus 5 |
|---|---|---|
| Input (/ 1M tokens) | $0.20 | $5.00 |
| Output (/ 1M tokens) | $1.20 | $25.00 |
| Cached input | $0.02 | $0.50 |
| Context window | 1,048,576 tokens | 1,000,000 tokens |
| Max output | 128,000 tokens | 128,000 tokens |
| Native reasoning | Yes | Yes |
| Knowledge cutoff | 2026-02 | 2026-05 |
| Relative latency | low | medium |
| Open weights | No | No |
| API model ID | gpt-5.6-luna | claude-opus-5 |
| Status | stable | stable |
GPT-5.6 Luna: Cut 80% from the $1/$6 launch price on 2026-07-30.
Choose GPT-5.6 Luna if…
- Classification and content moderation
- High-frequency agent subtasks
- Bulk summarization
- Cost-sensitive chat features
Choose Claude Opus 5 if…
- Agentic engineering with a cost ceiling
- Deep research and analysis
- Test-time compute scaling
- Production assistants needing recent knowledge
Frequently asked
Is GPT-5.6 Luna or Claude Opus 5 cheaper?
GPT-5.6 Luna is cheaper. On a blended 3:1 input-to-output workload it costs about 22.2x less than Claude Opus 5.
Which has the larger context window, GPT-5.6 Luna or Claude Opus 5?
GPT-5.6 Luna has the larger window at 1.05M tokens versus 1M.
Should I use GPT-5.6 Luna or Claude Opus 5?
Pick GPT-5.6 Luna for high-volume work on a tight budget. Pick Claude Opus 5 for most teams' best claude starting point. If cost dominates the decision, GPT-5.6 Luna wins; if you need the capability ceiling, benchmark both on your own evals before committing.