GPT-5.6 Luna vs Muse Spark 1.3 Contributor
Pricing, context window and real answers (September 2026)
GPT-5.6 Luna (OpenAI) and Muse Spark 1.3 Contributor (Meta), compared as you can actually call them on FastMetal. Both are served from the same OpenAI-compatible endpoint and API key; switching is a change to the model string.
Specs and pricing
 GPT-5.6 Luna |  Muse Spark 1.3 Contributor | |
|---|---|---|
| Provider | OpenAI | Meta |
| Input (per 1M tokens) | ¥35.74 | ¥17.59 |
| Output (per 1M tokens) | ¥214.44 | ¥35.18 |
| Typical cost (1,000 in + 500 out tokens × 1,000 calls) | ¥143 | ¥35 |
| Context window | 1,050,000 tokens | 1,048,576 tokens |
| Release date | 7/9/2026 | 9/2/2026 |
| Input modalities | file, image, text | text, image, video, file, audio |
| Throughput (p50) | — | — |
| Arena · overall | #67 · ELO 1,452 | Unranked |
| Arena · Japanese | #42 · ELO 1,439 | Unranked |
| Arena · coding | #71 · ELO 1,498 | Unranked |
Prices are FastMetal's yen rates before tax. Arena ranks are as of the latest leaderboard scrape.
Which should you pick?
- On price, Muse Spark 1.3 Contributor: ¥35.18 per 1M output tokens, 84% less than GPT-5.6 Luna.
- For long documents, GPT-5.6 Luna: a 1,050,000-token context window against 1,048,576 for Muse Spark 1.3 Contributor.
- If in doubt, try both on the same key. Switching is a change to the model string, and each is billed at its own rate.
Frequently asked questions
- Which is cheaper, GPT-5.6 Luna or Muse Spark 1.3 Contributor?
- Per 1M output tokens, GPT-5.6 Luna is ¥214.44 and Muse Spark 1.3 Contributor is ¥35.18 on FastMetal (yen, before tax), so Muse Spark 1.3 Contributor is cheaper.
- How do the context windows of GPT-5.6 Luna and Muse Spark 1.3 Contributor compare?
- GPT-5.6 Luna takes 1,050,000 tokens; Muse Spark 1.3 Contributor takes 1,048,576.
- Can I use GPT-5.6 Luna and Muse Spark 1.3 Contributor with the same API key?
- Yes. On FastMetal's OpenAI-compatible endpoint, switch by passing "gpt-5.6-luna" or "muse-spark-1.3-contributor" as the model. Each is billed at its own rate from the same prepaid balance.
Try both on one API key
Create an account and add credit to call GPT-5.6 Luna and Muse Spark 1.3 Contributor from the browser chat and the API. No monthly fee.
More comparisons with GPT-5.6 Luna
More comparisons with Muse Spark 1.3 Contributor
- Muse Spark 1.3 Contributor vs Claude Opus 5
- Muse Spark 1.3 Contributor vs Claude Sonnet 5
- Muse Spark 1.3 Contributor vs Claude Fable 5.1
- Muse Spark 1.3 Contributor vs Claude Fable 5
- Muse Spark 1.3 Contributor vs Claude Opus 4.8
- Muse Spark 1.3 Contributor vs Claude Haiku 4.5
- Muse Spark 1.3 Contributor details