# Aider setup: OPENAI_API_BASE and the openai/ model prefix

> Run Aider through our OpenAI-compatible endpoint: set OPENAI_API_BASE and OPENAI_API_KEY, launch with openai/<model>, save it in .aider.conf.yml and fix errors.

Source: https://oneaiapikey.com/docs/guides/aider

Base URL: `https://api.oneaiapikey.com/v1`

Aider is a terminal pair-programmer that edits files in your git repo and commits as it goes. It reaches models through LiteLLM, which supports any OpenAI-compatible endpoint. Two environment variables and a model prefix are all it takes to run Aider on our gateway, with every token billed from your prepaid balance.

## What you need

- Aider installed (for example with `python -m pip install aider-install` followed by `aider-install`, or your preferred method) and a git repository to work in.
- A funded account; top-ups start at $3: [create one](https://oneaiapikey.com/console/sign-up).
- An API key from the [API keys page](https://oneaiapikey.com/console/keys) (it begins with `sk-`).

## Step 1: point Aider at the gateway

Aider reads the standard OpenAI variables. Set the base URL **with** `/v1`:

macOS / Linux / Git Bash:

```bash
export OPENAI_API_BASE=https://api.oneaiapikey.com/v1
export OPENAI_API_KEY=sk-your-key-here
```

Windows:

```powershell
setx OPENAI_API_BASE "https://api.oneaiapikey.com/v1"
setx OPENAI_API_KEY "sk-your-key-here"
# then close this window and open a new terminal
```

`setx` writes the variables permanently but only for terminals opened afterwards, so restart your terminal before the next step. To keep the variables only for the current PowerShell window, use `$env:OPENAI_API_BASE = "..."` instead.

## Step 2: launch with the openai/ prefix

The `openai/` prefix is important. It tells Aider (via LiteLLM) to send the request in OpenAI format to whatever `OPENAI_API_BASE` says, instead of trying to reach a vendor’s own API. Everything after the prefix is the exact model id from our catalogue:

Start Aider:

```bash
aider --model openai/claude-sonnet-5
```

Aider uses a second, cheaper “weak” model for commit messages and chat summaries. Point it at a fast model so those calls don’t run on your flagship. You can also pass the base URL as a flag rather than an environment variable:

Main and weak model:

```bash
aider --model openai/claude-sonnet-5 \
  --weak-model openai/claude-haiku-4-5 \
  --openai-api-base https://api.oneaiapikey.com/v1
```

## Step 3: save it in .aider.conf.yml

Typing flags every time gets old. Aider reads `.aider.conf.yml` from your home directory and from the root of the current repo, so put your defaults there:

.aider.conf.yml:

```yaml
# ~/.aider.conf.yml  (or .aider.conf.yml in your repo root)
openai-api-base: https://api.oneaiapikey.com/v1
model: openai/claude-sonnet-5
weak-model: openai/claude-haiku-4-5
# keep the key in OPENAI_API_KEY rather than in this file
```

Keep `OPENAI_API_KEY` in your environment (or a `.env` file that is gitignored). Don’t commit keys to a repository config.

## Recommended models

Aider’s edit formats reward strong instruction following. Rates are USD per 1M tokens:

| Aider model | Good for | Input | Output |
| --- | --- | --- | --- |
| `openai/claude-sonnet-5` | Daily coding, Code review, Writing | $2.20 | $11 |
| `openai/claude-opus-5-5` | Agentic coding, Large refactors, Complex reasoning | $4.40 | $22 |
| `openai/gpt-6.1-sol` | Codex CLI, Tool calling, Long context | $2.20 | $11 |
| `openai/claude-haiku-4-5` | Sub-agents, Extraction, Chat | $1.10 | $5.50 |
| `openai/deepseek-v4-flash` | Budget coding, Sub-agents, Batch jobs | $0.24 | $0.96 |

Use `/model openai/<id>` inside a session to switch on the fly. The full catalogue is on the [models page](https://oneaiapikey.com/models).

## Step 4: verify it works

Launch Aider in a repo and ask something read-only, such as “What does this project do?”. A normal answer means the connection works, and the request appears in your console’s usage log. Aider’s own startup banner shows the main and weak model names, which is a quick way to confirm the prefix was applied.

## About the “unknown model” warning

Because our model ids aren’t in LiteLLM’s built-in database, Aider may print a warning that it doesn’t know the model’s context window or cost. The model still works. You can silence the warning with `--no-show-model-warnings`, or register the model’s limits and prices in a `.aider.model.metadata.json` file as described in Aider’s documentation on model warnings. Remember that the cost Aider prints is only an estimate: your console’s usage log shows what was actually charged.

## Troubleshooting

**401 / AuthenticationError.** `OPENAI_API_KEY` is missing or wrong in the shell that started Aider. Run `echo $OPENAI_API_KEY` (or `$env:OPENAI_API_KEY` in PowerShell) to check, re-copy the key from the console, and open a new terminal after `setx`.

**Requests go to OpenAI instead of the gateway.** `OPENAI_API_BASE` isn’t set in this shell, or a config file overrides it. Pass `--openai-api-base` explicitly to rule that out.

**404 Not Found.** The base URL lacks `/v1` or includes an endpoint path. Use exactly `https://api.oneaiapikey.com/v1`.

**“LLM Provider NOT provided” or model not found.** You left off the `openai/` prefix, or the id after it doesn’t match the catalogue. It must look like `openai/claude-sonnet-5`.

**Timeouts on large edits.** Aider streams by default; if you disabled it with `--no-stream`, re-enable streaming. Proxies cut idle non-streaming requests at roughly 100 seconds, so streaming matters for long outputs.

## Next steps

Want a more autonomous agent? Try [Claude Code](https://oneaiapikey.com/docs/guides/claude-code) or [OpenCode](https://oneaiapikey.com/docs/guides/opencode), or see all [tool guides](https://oneaiapikey.com/docs/guides). Per-model rates are on the [pricing page](https://oneaiapikey.com/pricing).

## Other OpenAI format tools

- [Codex CLI CLI](https://oneaiapikey.com/docs/guides/codex-cli)
- [Cursor IDE](https://oneaiapikey.com/docs/guides/cursor)
- [Cline Extension](https://oneaiapikey.com/docs/guides/cline)