Claude Opus 4.7 vs GPT-5.6 Luna
Pricing, context window and real answers (August 2026)
Claude Opus 4.7 (Anthropic) and GPT-5.6 Luna (OpenAI), 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
 Claude Opus 4.7 |  GPT-5.6 Luna | |
|---|---|---|
| Provider | Anthropic | OpenAI |
| Input (per 1M tokens) | ¥840 | ¥35.74 |
| Output (per 1M tokens) | ¥4,200 | ¥214.44 |
| Typical cost (1,000 in + 500 out tokens × 1,000 calls) | ¥2,940 | ¥143 |
| Context window | 1,000,000 tokens | 1,050,000 tokens |
| Release date | 4/16/2026 | 7/9/2026 |
| Input modalities | text, image, file | file, image, text |
| Arena · overall | #6 · ELO 1,494 | #63 · ELO 1,452 |
| Arena · Japanese | #18 · ELO 1,478 | #36 · ELO 1,444 |
| Arena · coding | #4 · ELO 1,547 | #69 · ELO 1,496 |
Prices are FastMetal's yen rates before tax. Arena ranks are as of the latest leaderboard scrape.
Which should you pick?
- On price, GPT-5.6 Luna: ¥214.44 per 1M output tokens, 95% less than Claude Opus 4.7.
- On the Overall arena board, Claude Opus 4.7 ranks higher (#6; GPT-5.6 Luna is #63).
- On the Japanese arena board, Claude Opus 4.7 ranks higher (#18; GPT-5.6 Luna is #36).
- On the Coding arena board, Claude Opus 4.7 ranks higher (#4; GPT-5.6 Luna is #69).
- For long documents, GPT-5.6 Luna: a 1,050,000-token context window against 1,000,000 for Claude Opus 4.7.
- 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, Claude Opus 4.7 or GPT-5.6 Luna?
- Per 1M output tokens, Claude Opus 4.7 is ¥4,200 and GPT-5.6 Luna is ¥214.44 on FastMetal (yen, before tax), so GPT-5.6 Luna is cheaper.
- How do the context windows of Claude Opus 4.7 and GPT-5.6 Luna compare?
- Claude Opus 4.7 takes 1,000,000 tokens; GPT-5.6 Luna takes 1,050,000.
- Which ranks higher, Claude Opus 4.7 or GPT-5.6 Luna?
- Claude Opus 4.7 ranks higher on the public arena (Claude Opus 4.7 #18, GPT-5.6 Luna #36). Ranks move as the leaderboard updates.
- Can I use Claude Opus 4.7 and GPT-5.6 Luna with the same API key?
- Yes. On FastMetal's OpenAI-compatible endpoint, switch by passing "anthropic-claude-opus-4-7" or "gpt-5.6-luna" 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 Claude Opus 4.7 and GPT-5.6 Luna from the browser chat and the API. No monthly fee.