Streaming SSE Events - Phaseo Docs

All streaming endpoints use SSE-style frames: data: <json-or-sentinel>

Typical frame sequence

One or more progress/delta frames.
A completion frame with final status and usage.
data: [DONE] sentinel.

JavaScript parser example

for await (const line of client.streamText({
  model: "openai/gpt-5-nano",
  messages: [{ role: "user", content: "Say hello." }],
  stream: true,
})) {
  if (!line.startsWith("data:")) continue;
  const payload = line.slice(5).trim();
  if (payload === "[DONE]") break;
  console.log(payload);
}

Python parser example

for line in client.stream_response({
    "model": "openai/gpt-5-nano",
    "input": "Say hello.",
    "stream": True,
}):
    if not line.startswith("data:"):
        continue
    payload = line[5:].strip()
    if payload == "[DONE]":
        break
    print(payload)

Endpoint format notes

/v1/chat/completions: chunked choices[].delta style events.
/v1/responses: responses-style output item/delta events.
/v1/messages: Anthropic-style events (message_start, content_block_delta, message_stop).

Last modified on July 26, 2026