gpt-oss-120b vs Muse Spark 1.3 Contributor
Pricing, context window and real answers (September 2026)
gpt-oss-120b (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-oss-120b |  Muse Spark 1.3 Contributor | |
|---|---|---|
| Provider | OpenAI | Meta |
| Input (per 1M tokens) | ¥16 | ¥17.59 |
| Output (per 1M tokens) | ¥79 | ¥35.18 |
| Typical cost (1,000 in + 500 out tokens × 1,000 calls) | ¥56 | ¥35 |
| Context window | 131,072 tokens | 1,048,576 tokens |
| Release date | 8/5/2025 | 9/2/2026 |
| Input modalities | text | text, image, video, file, audio |
| Throughput (p50) | — | — |
| Arena · overall | #201 · ELO 1,352 | Unranked |
| Arena · Japanese | #136 · ELO 1,328 | Unranked |
| Arena · coding | #208 · ELO 1,391 | 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, 55% less than gpt-oss-120b.
- For long documents, Muse Spark 1.3 Contributor: a 1,048,576-token context window against 131,072 for gpt-oss-120b.
- 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-oss-120b or Muse Spark 1.3 Contributor?
- Per 1M output tokens, gpt-oss-120b is ¥79 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-oss-120b and Muse Spark 1.3 Contributor compare?
- gpt-oss-120b takes 131,072 tokens; Muse Spark 1.3 Contributor takes 1,048,576.
- Can I use gpt-oss-120b and Muse Spark 1.3 Contributor with the same API key?
- Yes. On FastMetal's OpenAI-compatible endpoint, switch by passing "gpt-oss-120b" 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-oss-120b and Muse Spark 1.3 Contributor from the browser chat and the API. No monthly fee.
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