What's the difference between streaming and non-streaming calls?

from openai import OpenAI

client = OpenAI(
    api_key="sk-your-apiyi-key",
    base_url="https://api.apiyi.com/v1",
)

stream = client.chat.completions.create(
    model="gpt-5.4",
    messages=[{"role": "user", "content": "Explain quantum computing"}],
    stream=True,
    stream_options={"include_usage": True},   # without this, no usage
    timeout=120,
)

chunks = []
for chunk in stream:
    # the final usage chunk has an empty choices array — check before indexing
    if chunk.choices and chunk.choices[0].delta.content:
        piece = chunk.choices[0].delta.content
        chunks.append(piece)
        print(piece, end="", flush=True)
    if chunk.usage:
        print(f"\nUsage: {chunk.usage.total_tokens} tokens")

full_text = "".join(chunks)   # assemble it yourself if you need the whole thing

import OpenAI from "openai";

const client = new OpenAI({
  apiKey: "sk-your-apiyi-key",
  baseURL: "https://api.apiyi.com/v1",
});

const stream = await client.chat.completions.create({
  model: "gpt-5.4",
  messages: [{ role: "user", content: "Explain quantum computing" }],
  stream: true,
  stream_options: { include_usage: true },
});

let full = "";
for await (const chunk of stream) {
  const delta = chunk.choices?.[0]?.delta?.content;
  if (delta) {
    full += delta;
    process.stdout.write(delta);
  }
  if (chunk.usage) console.log("\nUsage:", chunk.usage.total_tokens);
}

# Non-streaming: one complete JSON
curl https://api.apiyi.com/v1/chat/completions \
  -H "Authorization: Bearer $APIYI_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "gpt-5.4",
    "messages": [{"role": "user", "content": "Hello"}]
  }'

# Streaming: a series of data: chunks, ending with data: [DONE]
# -N disables curl's own buffering, otherwise it still looks like one blob
curl -N https://api.apiyi.com/v1/chat/completions \
  -H "Authorization: Bearer $APIYI_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "gpt-5.4",
    "messages": [{"role": "user", "content": "Hello"}],
    "stream": true,
    "stream_options": {"include_usage": true}
  }'