Streaming

With "stream": true the response is a text/event-stream: the answer arrives in chunks as the model generates it.

curl -N https://router.nodul.ru/api/v1/chat/completions \
  -H "Authorization: Bearer $NODUL_ROUTER_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"model": "google/gemma-3-4b-it", "stream": true, "messages": [{"role": "user", "content": "Count to five."}]}'

import os
from openai import OpenAI

client = OpenAI(base_url="https://router.nodul.ru/api/v1", api_key=os.environ["NODUL_ROUTER_API_KEY"])
stream = client.chat.completions.create(
    model="google/gemma-3-4b-it",
    messages=[{"role": "user", "content": "Count to five."}],
    stream=True,
)
for chunk in stream:
    if chunk.choices and chunk.choices[0].delta.content:
        print(chunk.choices[0].delta.content, end="", flush=True)
    if chunk.usage:
        print("\ncost:", chunk.usage.cost)

import OpenAI from "openai";

const client = new OpenAI({ baseURL: "https://router.nodul.ru/api/v1", apiKey: process.env.NODUL_ROUTER_API_KEY });
const stream = await client.chat.completions.create({
  model: "google/gemma-3-4b-it",
  messages: [{ role: "user", content: "Count to five." }],
  stream: true,
});
for await (const chunk of stream) {
  process.stdout.write(chunk.choices[0]?.delta?.content ?? "");
  if (chunk.usage) console.log("\ncost:", chunk.usage.cost);
}

Events

: keepalive

data: {"id":"gen-…","object":"chat.completion.chunk","model":"google/gemma-3-4b-it","choices":[{"index":0,"delta":{"role":"assistant","content":"One"}}]}

data: {"id":"gen-…","object":"chat.completion.chunk","choices":[{"index":0,"delta":{"content":", two"},"finish_reason":null}]}

data: {"id":"gen-…","object":"chat.completion.chunk","choices":[{"index":0,"delta":{},"finish_reason":"stop"}]}

data: {"id":"gen-…","object":"chat.completion.chunk","choices":[],"usage":{"prompt_tokens":12,"completion_tokens":9,"total_tokens":21,"cost":0.0000081}}

data: [DONE]

• Lines that start with : are comments that keep the connection alive. SSE clients ignore them; a hand-written parser must skip them.
• Every chunk has the generation id; the response header X-Generation-Id carries it too.
• delta.content holds text, delta.tool_calls holds tool calls in pieces, and reasoning models may send delta.reasoning or delta.reasoning_content.
• The last chunk before data: [DONE] has usage with cost in PnP. You do not need stream_options: the router always asks for it.

Errors in a stream

Errors before the first chunk come as a normal HTTP error with a JSON body, see Errors. Once the stream has started the status is already 200, so a failure comes as an event:

data: {"error":{"code":504,"message":"the upstream stream timed out (idle)"},"choices":[{"index":0,"delta":{},"finish_reason":"error"}]}

The router never switches to a fallback model after the first chunk: the partial answer is not regenerated elsewhere. If the connection ends without [DONE], treat the answer as incomplete.

Timeouts

Use streaming for long answers and reasoning models: a non-streamed request also has to start within 120 seconds and finish within 10 minutes.

Cancelling

Close the connection to stop generation. The request is billed for what was generated up to that moment, by the provider's usage report or, when there is none, by an estimate.