Best LLM APIs for instruction following (October 2026)
The models rated highest at following detailed instructions and formats, restricted to what FastMetal serves today.
Ranked by ELO on the public arena's Instruction Following board, restricted to models FastMetal serves. The order updates with the leaderboard.
Rankings: LMArena leaderboard dataset (lmarena-ai/leaderboard-dataset), CC BY 4.0, snapshot 2026-10-08; category names mapped and ratings rounded by FastMetal.
| Links | |||||||
|---|---|---|---|---|---|---|---|
| 1 | Claude Opus 5.5 |  Anthropic | #2 · 1,519 | $4.22 | $21.10 | 1,000,000 | DetailsCompare |
| 2 | Claude Opus 5 | Anthropic | #2 · 1,519 | $5.28 | $26.38 | 1,000,000 | DetailsCompare |
| 3 | Claude Fable 5 | Anthropic | #4 · 1,509 | $10.55 | $52.75 | 1,000,000 | DetailsCompare |
| 4 | Claude Opus 4.6 | Anthropic | #6 · 1,499 | $5.42 | $26.77 | 1,000,000 | DetailsCompare |
| 5 | Claude Fable 5.1 | Anthropic | #7 · 1,498 | $10.55 | $52.75 | 1,000,000 | DetailsCompare |
| 6 | GPT-5.6 Sol |  OpenAI | #12 · 1,490 | $2.20 | $11.00 | 1,050,000 | DetailsCompare |
| 7 | Claude Sonnet 5.5 | Anthropic | #13 · 1,489 | $2.11 | $10.55 | 1,000,000 | DetailsCompare |
| 8 | Claude Sonnet 5 | Anthropic | #13 · 1,489 | $2.11 | $10.55 | 1,000,000 | DetailsCompare |
| 9 | Gemini 3.8 Flash |  Google | #14 · 1,488 | $0.7913 | $3.96 | 1,048,576 | DetailsCompare |
| 10 | GPT-6.1 Sol | OpenAI | #15 · 1,488 | $2.11 | $10.55 | 1,050,000 | DetailsCompare |
Click a column heading to re-sort; the table opens in this category's ranking order. Prices are per 1M tokens, before tax; context is in tokens.
Frequently asked questions
- What is this ranking based on?
- Ranked by ELO on the public arena's Instruction Following board, restricted to models FastMetal serves. The order updates with the leaderboard.
- How is pricing decided?
- Each model has a price per 1M tokens (before tax) — in yen, or in US dollars on a US-dollar account — drawn from a prepaid balance as you use it. There is no subscription or monthly fee.
- Can I use the top models with one API key?
- Yes. Every model on this page is served from FastMetal's OpenAI-compatible endpoint under one API key; switching is a change to the model string.
Every model above runs on one API key
Create an account and add credit to call these models from the browser chat and the API. No monthly fee.