Comparison
GPT-family models: FastMetal vs contracting OpenAI directly
FastMetal's API is OpenAI-compatible, so OpenAI's official SDK and compatible tools work as they are, with only the base URL and API key changed. The catalog includes GPT-family models, and the lineup is expanding.
To be upfront: FastMetal is not a replacement for everything OpenAI offers. Fine-tuning, the Realtime API, and other official-only features need a direct contract. FastMetal is the option when chat completions are the core of your usage and you want JPY billing and cross-provider model comparison.
At a glance
| Aspect | FastMetal | OpenAI direct |
|---|---|---|
| Billing and invoices | Prepaid in JPY. Qualified invoices | Billed in USD |
| API compatibility | OpenAI-compatible. The official SDK and compatible tools work unchanged | The official API, with every endpoint |
| Models and providers | Models from many providers, including GPT-family. Lineup expanding | Every OpenAI model and feature |
| Operational burden | Many providers, one account | Simple if OpenAI is your only provider |
| Language and support | Japanese UI, docs, and support | Primarily English |
| Data flow | Requests are relayed to each provider | Requests go directly to OpenAI |
When going direct fits
- You need official features beyond chat completions: fine-tuning, the Realtime API, Assistants.
- You want OpenAI's newest models on day one.
- Your volume is large enough to negotiate discounts directly with OpenAI.
When FastMetal fits
- Chat completions are the core of your usage, and you need JPY billing and qualified invoices.
- You want GPT-family models next to Claude, Gemini, and other providers' models, on one key.
- You want to keep your OpenAI SDK code unchanged. The switch is one line: the base URL.
See the models page for the GPT-family models currently on FastMetal. If you need official-only features, running FastMetal alongside a direct contract is a realistic setup.
This comparison reflects August 2026.
Try it by changing one line: the base URL
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