Cursor

Use FastMetal models as the model behind Cursor's chat and agent. Cursor takes a FastMetal API key in its own API key settings, with a FastMetal base URL built for the requests Cursor sends.

Requirements

A Cursor Premium, Super or Ultra plan, and a FastMetal API key. Cursor offers its own-API-key setting (BYOK) only on those plans: Free and Plus cannot use it. This is a restriction of Cursor's plans, and no FastMetal setting changes it.

1. Create an API key

Create or reveal a key on the API keys page. It is shown once, so paste it somewhere safe.

Open API keys

2. Add the key to Cursor

Open Cursor's Settings, go to Models, and under API Keys turn on OpenAI API Key. Paste your FastMetal API key there.

3. Point the base URL at FastMetal

On the same screen, turn on Override OpenAI Base URL and enter the URL below exactly as shown, with no /v1 and no trailing slash.

https://api.fastmetal.ai/cursor

Cursor sends requests shaped like OpenAI's Responses API to the chat completions path and expects chat completions back. The /cursor base URL accepts that shape. The standard /v1 base URL rejects it, so Cursor shows an error there.

4. Add the models

In the Models list, choose Add Custom Model and enter a FastMetal model id. The Claude models below have been checked with Cursor's request format, including streamed answers and tool calls.

anthropic-claude-sonnet-5-5
anthropic-claude-opus-5-5
anthropic-claude-haiku-5-5

Other models in the FastMetal catalog can be added the same way. Whether they work in Cursor depends on the host that serves them, so check each one with a short chat before relying on it in the agent.

Model ids must match the gateway exactly

Take the id from the code sample on a model's page, or from the list below. A page URL is not the id: it swaps dots for dashes. Do not add a provider prefix such as openai/. The router name auto cannot be used from Cursor.

List every id your key can use (this also confirms the key and the base URL):

curl https://api.fastmetal.ai/cursor/models \
  -H "Authorization: Bearer your-api-key"

5. Pick the model

Select the FastMetal model in the model picker of Cursor's chat or agent. Each request is billed to your key per token, at the price on the model's page, and appears on your usage page.

What Cursor keeps on its own models

Tab completion always uses Cursor's own model.
Cursor does not send your own key for Auto, Cloud and Background Agents, Automations or the Cursor CLI. Those keep using Cursor's models.
Pick a specific FastMetal model. FastMetal's auto router name is refused on this base URL.
While Override OpenAI Base URL is on, Cursor also sends its built-in OpenAI models to this URL. Turn the override off to go back to Cursor's own models.

For approvers and finance

Usage from Cursor comes out of the same prepaid balance as every other FastMetal API call and appears on the same usage page and invoice. Cursor sends a long system prompt with every request, so agent work uses more tokens than a plain chat. The Cursor plan itself is paid to Cursor and is separate from the FastMetal bill.