vLLM can serve open-source (and some custom) models via an OpenAI-compatible HTTP API. Genesis connects to vLLM using the openai-completions API.

Genesis can also auto-discover available models from vLLM when you opt in with VLLM_API_KEY (any value works if your server does not enforce auth) and you do not define an explicit models.providers.vllm entry.

Genesis treats vllm as a local OpenAI-compatible provider that supports streamed usage accounting, so status/context token counts can update from stream_options.include_usage responses.

Getting started

Start vLLM with an OpenAI-compatible server

Your base URL should expose `/v1` endpoints (e.g. `/v1/models`, `/v1/chat/completions`). vLLM commonly runs on:

```
http://127.0.0.1:8000/v1
```

Set the API key environment variable

Any value works if your server does not enforce auth:

```bash
export VLLM_API_KEY="vllm-local"
```

Select a model

Replace with one of your vLLM model IDs:

```json5
{
  agents: {
    defaults: {
      model: { primary: "vllm/your-model-id" },
    },
  },
}
```

Verify the model is available

```bash
genesis models list --provider vllm
```

Model discovery (implicit provider)

When VLLM_API_KEY is set (or an auth profile exists) and you do not define models.providers.vllm, Genesis queries:

GET http://127.0.0.1:8000/v1/models

and converts the returned IDs into model entries.

Explicit configuration (manual models)

Use explicit config when:

• vLLM runs on a different host or port
• You want to pin contextWindow or maxTokens values
• Your server requires a real API key (or you want to control headers)

{
  models: {
    providers: {
      vllm: {
        baseUrl: "http://127.0.0.1:8000/v1",
        apiKey: "${VLLM_API_KEY}",
        api: "openai-completions",
        models: [
          {
            id: "your-model-id",
            name: "Local vLLM Model",
            reasoning: false,
            input: ["text"],
            cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0 },
            contextWindow: 128000,
            maxTokens: 8192,
          },
        ],
      },
    },
  },
}

Advanced configuration

Proxy-style behavior

vLLM is treated as a proxy-style OpenAI-compatible `/v1` backend, not a native
OpenAI endpoint. This means:

| Behavior | Applied? |
|----------|----------|
| Native OpenAI request shaping | No |
| `service_tier` | Not sent |
| Responses `store` | Not sent |
| Prompt-cache hints | Not sent |
| OpenAI reasoning-compat payload shaping | Not applied |
| Hidden Genesis attribution headers | Not injected on custom base URLs |

Custom base URL

If your vLLM server runs on a non-default host or port, set `baseUrl` in the explicit provider config:

```json5
{
  models: {
    providers: {
      vllm: {
        baseUrl: "http://192.168.1.50:9000/v1",
        apiKey: "${VLLM_API_KEY}",
        api: "openai-completions",
        models: [
          {
            id: "my-custom-model",
            name: "Remote vLLM Model",
            reasoning: false,
            input: ["text"],
            contextWindow: 64000,
            maxTokens: 4096,
          },
        ],
      },
    },
  },
}
```

Troubleshooting

Server not reachable

Check that the vLLM server is running and accessible:

```bash
curl http://127.0.0.1:8000/v1/models
```

If you see a connection error, verify the host, port, and that vLLM started with the OpenAI-compatible server mode.

Auth errors on requests

If requests fail with auth errors, set a real `VLLM_API_KEY` that matches your server configuration, or configure the provider explicitly under `models.providers.vllm`.

<div class="callout tip">
If your vLLM server does not enforce auth, any non-empty value for `VLLM_API_KEY` works as an opt-in signal for Genesis.
</div>

No models discovered

Auto-discovery requires `VLLM_API_KEY` to be set **and** no explicit `models.providers.vllm` config entry. If you have defined the provider manually, Genesis skips discovery and uses only your declared models.

Related

• Model selection Choosing providers, model refs, and failover behavior.

• OpenAI Native OpenAI provider and OpenAI-compatible route behavior.

• OAuth and auth Auth details and credential reuse rules.

• Troubleshooting Common issues and how to resolve them.