Streaming

Use a current public model ID from Models or GET /models. Example IDs and options must match the selected model’s advertised capabilities and limits.

Set "stream": true to receive the completion as server-sent events, token by token, in the standard OpenAI chunk format.

Enabling streaming

Python
curl

stream = client.chat.completions.create(
    model="nomask-1.2",
    messages=[{"role": "user", "content": "Write a haiku about the sea."}],
    stream=True,
    stream_options={"include_usage": True},
)
for chunk in stream:
    delta = chunk.choices[0].delta if chunk.choices else None
    if delta and delta.content:
        print(delta.content, end="", flush=True)

curl -N https://nomask.ai/api/v1/chat/completions \
  -H "Authorization: Bearer $NOMASK_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "nomask-1.2",
    "messages": [{"role": "user", "content": "Write a haiku about the sea."}],
    "stream": true,
    "stream_options": {"include_usage": true}
  }'

The chunk stream

The response is text/event-stream. Each event is a chat.completion.chunk object, and the stream ends with data: [DONE]:

data: {"id":"chatcmpl_...","object":"chat.completion.chunk","choices":[{"delta":{"role":"assistant"},"index":0}]}

data: {"id":"chatcmpl_...","object":"chat.completion.chunk","choices":[{"delta":{"content":"Waves"},"index":0}]}

data: {"id":"chatcmpl_...","object":"chat.completion.chunk","choices":[{"delta":{"content":" fold"},"index":0}]}

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

data: [DONE]

Reasoning tokens arrive as delta.reasoning_content, interleaved before the answer. See Reasoning.

Usage and cost on streams

Pass "stream_options": {"include_usage": true} and the final data chunk before [DONE] has an empty choices array and carries the totals:

{
  "object": "chat.completion.chunk",
  "choices": [],
  "usage": {"prompt_tokens": 14, "completion_tokens": 21, "total_tokens": 35},
  "nomask": {
    "model_cost_usd": 0.000049,
    "cost_usd": 0.000049
  }
}

nomask.cost_usd is the exact USD amount charged to your balance for the request, the same figure GET /usage will show. Confirmed cached input and frozen savings are included in the usage metadata. See Prompt Caching for the response fields and billing rules.

Errors mid-stream

If the model fails after the stream has started, you receive a final chunk containing an error object in the standard envelope, then [DONE]. Errors before any tokens are sent return a normal JSON error response with the right HTTP status instead.

Disconnects and billing

Billing settles when the request finishes on the server. If your client disconnects mid-stream, the tokens generated up to that point are still billed; when exact usage is unavailable for an interrupted stream, token counts are estimated and the usage record is flagged with tokens_estimated: true.

Docs

Getting Started

Text & Chat

Image

Production

Coding Tools

Chat API

Image API

Model API

Account & Usage

Errors & Limits

Enabling streaming

The chunk stream

Usage and cost on streams

Errors mid-stream

Disconnects and billing

​Enabling streaming

​The chunk stream

​Usage and cost on streams

​Errors mid-stream

​Disconnects and billing

Enabling streaming

The chunk stream

Usage and cost on streams

Errors mid-stream

Disconnects and billing