API Reference

Developer note: This guide is for people writing code or integrating with Lumen programmatically. If you just want to use the chat interface, you don't need this page.

Lumen exposes an OpenAI-compatible REST API at /v1/. Any tool or library that works with OpenAI can be pointed at your Lumen instance with minimal changes.

Base URL and Authentication

Replace https://your-lumen-instance with your institution's Lumen URL. All requests require an Authorization header:

Authorization: Bearer sk_your_api_key_here

See Profile → API Keys to create a key.

Endpoints

Method	Path	Description
`GET`	`/v1/models`	List available models
`POST`	`/v1/chat/completions`	Send a chat message and receive a reply

List Models

curl https://your-lumen-instance/v1/models \
  -H "Authorization: Bearer sk_your_api_key_here"

Returns a list of model IDs you can use in chat completion requests.

Chat Completions

Basic request (curl)

curl https://your-lumen-instance/v1/chat/completions \
  -H "Authorization: Bearer sk_your_api_key_here" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "gpt-4o",
    "messages": [
      {"role": "user", "content": "Explain quantum entanglement in plain English"}
    ]
  }'

Python (openai SDK)

Install the library once: pip install openai

from openai import OpenAI

client = OpenAI(
    api_key="sk_your_api_key_here",
    base_url="https://your-lumen-instance/v1"
)

response = client.chat.completions.create(
    model="gpt-4o",
    messages=[
        {"role": "user", "content": "Explain quantum entanglement in plain English"}
    ]
)

print(response.choices[0].message.content)

Python — multi-turn conversation

from openai import OpenAI

client = OpenAI(
    api_key="sk_your_api_key_here",
    base_url="https://your-lumen-instance/v1"
)

history = []

def chat(user_message):
    history.append({"role": "user", "content": user_message})
    response = client.chat.completions.create(
        model="gpt-4o",
        messages=history
    )
    reply = response.choices[0].message.content
    history.append({"role": "assistant", "content": reply})
    return reply

print(chat("What is a transformer model?"))
print(chat("How does the attention mechanism work?"))

Python — streaming responses

from openai import OpenAI

client = OpenAI(
    api_key="sk_your_api_key_here",
    base_url="https://your-lumen-instance/v1"
)

with client.chat.completions.stream(
    model="gpt-4o",
    messages=[{"role": "user", "content": "Write a short poem about data science"}]
) as stream:
    for text in stream.text_stream:
        print(text, end="", flush=True)
print()

Python — system prompt

response = client.chat.completions.create(
    model="gpt-4o",
    messages=[
        {"role": "system", "content": "You are a helpful research assistant who always cites sources."},
        {"role": "user", "content": "Summarize recent advances in protein folding"}
    ]
)
print(response.choices[0].message.content)

Node.js (openai SDK)

Install the library once: npm install openai

import OpenAI from "openai";

const client = new OpenAI({
  apiKey: "sk_your_api_key_here",
  baseURL: "https://your-lumen-instance/v1",
});

const response = await client.chat.completions.create({
  model: "gpt-4o",
  messages: [
    { role: "user", content: "Explain quantum entanglement in plain English" }
  ],
});

console.log(response.choices[0].message.content);

Node.js — streaming

import OpenAI from "openai";

const client = new OpenAI({
  apiKey: "sk_your_api_key_here",
  baseURL: "https://your-lumen-instance/v1",
});

const stream = await client.chat.completions.stream({
  model: "gpt-4o",
  messages: [{ role: "user", content: "Write a haiku about machine learning" }],
});

for await (const chunk of stream) {
  const text = chunk.choices[0]?.delta?.content ?? "";
  process.stdout.write(text);
}

Using Lumen as a drop-in replacement for OpenAI

If you have existing code that uses the OpenAI API, you can redirect it to Lumen by changing two values:

# Before (standard OpenAI)
client = OpenAI(api_key="sk-...")

# After (Lumen)
client = OpenAI(
    api_key="sk_your_lumen_key",
    base_url="https://your-lumen-instance/v1"
)

Everything else — model names, message format, streaming, tool calls — works identically as long as the model you request is available in your Lumen instance.

Using Lumen in Third-Party Chat Tools

Many desktop and web chat applications support custom OpenAI-compatible endpoints. Look for a setting labelled API Base URL, Custom endpoint, or OpenAI-compatible server and enter:

https://your-lumen-instance/v1

Then paste your sk_... key as the API key. Common tools that support this pattern include Jan, Open WebUI, Msty, and most AI IDE extensions.

Token Usage in Responses

Every response includes a usage field with exact token counts:

{
  "choices": [...],
  "usage": {
    "prompt_tokens": 42,
    "completion_tokens": 183,
    "total_tokens": 225
  }
}

These counts drive the coin deduction on your account. You can retrieve the same numbers from the Usage page after the fact.

Rate Limits

If you send too many requests too quickly, the API returns:

HTTP 429 Too Many Requests

Wait a moment and retry. The Usage page shows your recent request volume so you can gauge how close you are to the limit.

Error Responses

HTTP Status	Meaning
`401`	Invalid or missing API key
`403`	Your account does not have access to the requested model
`404`	Model not found
`429`	Rate limit exceeded
`503`	Model backend is currently unavailable