Cursor with an OpenAI-Compatible Relay: Key Settings

§1 Connect Cursor to a relay without guessing

Using Cursor with an OpenAI-compatible relay can simplify access to multiple model providers, but the connection depends on more than pasting an API key. The base URL, exact model identifier, feature support, and network path all matter. This walkthrough explains what to configure and how to test each layer before trusting the setup for development work.

Fluxio fits this workflow when you want streaming responses and pay-per-token billing through one API key. Its relay provides access to multiple model families through an OpenAI-style interface. However, protocol compatibility does not automatically mean every Cursor feature will work with every routed model.

§2 Step 1: Create a key and check your data boundaries

Create a Fluxio API key and keep it out of source files, shared settings, screenshots, and committed environment files. Before sending repository context, review both Cursor’s and the relay’s current privacy, retention, and data-processing policies. A custom endpoint introduces another service into the path handling your prompts and code.

Check your available balance and any account-level usage controls. Relay usage is billed separately from your Cursor subscription, and supplying your own key does not necessarily replace subscription requirements for all Cursor features.

§3 Step 2: Find Cursor’s provider settings

Open Cursor Settings and locate the model or API-key configuration area. Labels and placement can change between releases. Look for the OpenAI API-key field and the option to override the OpenAI base URL, if your version exposes it.

• – API key: Enter your Fluxio key in the provider field associated with the overridden endpoint.
• – Base URL: Use https://api.fluxioapi.com/v1 for an OpenAI-style client configuration.
• – Provider activation: Enable the relevant key or provider setting if Cursor requires a separate toggle.

The relay’s API root is https://api.fluxioapi.com. The /v1 suffix belongs in an OpenAI-style base URL; do not append a full operation path such as /chat/completions. Also avoid duplicating /v1 if a configuration field explicitly adds it automatically.

§4 Step 3: Select an exact, supported model ID

Choose a model available in your relay account, then copy its exact API identifier from the relay’s current model listing. A display name such as Claude Haiku 4.5 or Gemini 2.5 Flash is not necessarily the string an API request expects.

If Cursor permits custom model entries, add the identifier there and select it for the conversation. Do not assume that choosing a similarly named built-in entry routes requests through your relay. Confirm the selected model and provider configuration before testing.

Start with one model rather than several. This makes it easier to distinguish a routing mistake from a capability mismatch. Only enable capability options that the selected model and relay route actually support.

§5 Step 4: Test streaming before agent workflows

Send a short, ordinary chat request first. Confirm that a response arrives and that usage appears in your relay account. Fluxio is streaming-first, so replies can arrive token by token, although visible rendering also depends on Cursor and any intermediate buffering.

Next, ask Cursor to explain a small function from your project. Finally, test a narrowly scoped edit or tool action. These checks exercise different layers: basic authentication, repository context, and structured tool interactions.

A successful chat response does not prove full agent compatibility. Tool calls, structured outputs, context limits, and endpoint support can differ across routes. Cursor features such as Tab completion may use separate infrastructure rather than your custom API configuration.

§6 Step 5: Troubleshoot the setting that matches the symptom

• – Authentication failure: Check for whitespace, an inactive key, or a key entered under the wrong provider.
• – Not found: Verify the base URL, version suffix, and exact model identifier.
• – Chat works but tools fail: Check the route’s tool support and Cursor’s current custom-provider limitations.
• – Delayed or interrupted output: Check rate limits, account balance, network stability, and proxy buffering.

Once the connection works, keep requests focused and monitor token usage. Large repository context and repeated agent steps can increase costs even when the initial prompt is short.

Sign up for Fluxio to try your Cursor relay setup.