sglang/docs/backend/openai_api_completions.ipynb

OpenAI APIs - Completions

SGLang provides OpenAI-compatible APIs to enable a smooth transition from OpenAI services to self-hosted local models. A complete reference for the API is available in the OpenAI API Reference.

This tutorial covers the following popular APIs:

• chat/completions
• completions
• batches

Check out other tutorials to learn about vision APIs for vision-language models and embedding APIs for embedding models.

Launch A Server

Launch the server in your terminal and wait for it to initialize.

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from sglang.test.test_utils import is_in_ci

if is_in_ci():
    from patch import launch_server_cmd
else:
    from sglang.utils import launch_server_cmd

from sglang.utils import wait_for_server, print_highlight, terminate_process


server_process, port = launch_server_cmd(
    "python -m sglang.launch_server --model-path meta-llama/Meta-Llama-3.1-8B-Instruct --host 0.0.0.0"
)

wait_for_server(f"http://localhost:{port}")
print(f"Server started on http://localhost:{port}")

Chat Completions

Usage

The server fully implements the OpenAI API. It will automatically apply the chat template specified in the Hugging Face tokenizer, if one is available. You can also specify a custom chat template with --chat-template when launching the server.

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import openai

client = openai.Client(base_url=f"http://127.0.0.1:{port}/v1", api_key="None")

response = client.chat.completions.create(
    model="meta-llama/Meta-Llama-3.1-8B-Instruct",
    messages=[
        {"role": "user", "content": "List 3 countries and their capitals."},
    ],
    temperature=0,
    max_tokens=64,
)

print_highlight(f"Response: {response}")

Parameters

The chat completions API accepts OpenAI Chat Completions API's parameters. Refer to OpenAI Chat Completions API for more details.

Here is an example of a detailed chat completion request:

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response = client.chat.completions.create(
    model="meta-llama/Meta-Llama-3.1-8B-Instruct",
    messages=[
        {
            "role": "system",
            "content": "You are a knowledgeable historian who provides concise responses.",
        },
        {"role": "user", "content": "Tell me about ancient Rome"},
        {
            "role": "assistant",
            "content": "Ancient Rome was a civilization centered in Italy.",
        },
        {"role": "user", "content": "What were their major achievements?"},
    ],
    temperature=0.3,  # Lower temperature for more focused responses
    max_tokens=128,  # Reasonable length for a concise response
    top_p=0.95,  # Slightly higher for better fluency
    presence_penalty=0.2,  # Mild penalty to avoid repetition
    frequency_penalty=0.2,  # Mild penalty for more natural language
    n=1,  # Single response is usually more stable
    seed=42,  # Keep for reproducibility
)

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

Streaming mode is also supported.

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stream = client.chat.completions.create(
    model="meta-llama/Meta-Llama-3.1-8B-Instruct",
    messages=[{"role": "user", "content": "Say this is a test"}],
    stream=True,
)
for chunk in stream:
    if chunk.choices[0].delta.content is not None:
        print(chunk.choices[0].delta.content, end="")

Completions

Usage

Completions API is similar to Chat Completions API, but without the messages parameter or chat templates.

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response = client.completions.create(
    model="meta-llama/Meta-Llama-3.1-8B-Instruct",
    prompt="List 3 countries and their capitals.",
    temperature=0,
    max_tokens=64,
    n=1,
    stop=None,
)

print_highlight(f"Response: {response}")

Parameters

The completions API accepts OpenAI Completions API's parameters. Refer to OpenAI Completions API for more details.

Here is an example of a detailed completions request:

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response = client.completions.create(
    model="meta-llama/Meta-Llama-3.1-8B-Instruct",
    prompt="Write a short story about a space explorer.",
    temperature=0.7,  # Moderate temperature for creative writing
    max_tokens=150,  # Longer response for a story
    top_p=0.9,  # Balanced diversity in word choice
    stop=["\n\n", "THE END"],  # Multiple stop sequences
    presence_penalty=0.3,  # Encourage novel elements
    frequency_penalty=0.3,  # Reduce repetitive phrases
    n=1,  # Generate one completion
    seed=123,  # For reproducible results
)

print_highlight(f"Response: {response}")

Structured Outputs (JSON, Regex, EBNF)

For OpenAI compatible structed outputs API, refer to Structured Outputs for more details.

Batches

Batches API for chat completions and completions are also supported. You can upload your requests in jsonl files, create a batch job, and retrieve the results when the batch job is completed (which takes longer but costs less).

The batches APIs are:

• batches
• batches/{batch_id}/cancel
• batches/{batch_id}

Here is an example of a batch job for chat completions, completions are similar.

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import json
import time
from openai import OpenAI

client = OpenAI(base_url=f"http://127.0.0.1:{port}/v1", api_key="None")

requests = [
    {
        "custom_id": "request-1",
        "method": "POST",
        "url": "/chat/completions",
        "body": {
            "model": "meta-llama/Meta-Llama-3.1-8B-Instruct",
            "messages": [
                {"role": "user", "content": "Tell me a joke about programming"}
            ],
            "max_tokens": 50,
        },
    },
    {
        "custom_id": "request-2",
        "method": "POST",
        "url": "/chat/completions",
        "body": {
            "model": "meta-llama/Meta-Llama-3.1-8B-Instruct",
            "messages": [{"role": "user", "content": "What is Python?"}],
            "max_tokens": 50,
        },
    },
]

input_file_path = "batch_requests.jsonl"

with open(input_file_path, "w") as f:
    for req in requests:
        f.write(json.dumps(req) + "\n")

with open(input_file_path, "rb") as f:
    file_response = client.files.create(file=f, purpose="batch")

batch_response = client.batches.create(
    input_file_id=file_response.id,
    endpoint="/v1/chat/completions",
    completion_window="24h",
)

print_highlight(f"Batch job created with ID: {batch_response.id}")

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while batch_response.status not in ["completed", "failed", "cancelled"]:
    time.sleep(3)
    print(f"Batch job status: {batch_response.status}...trying again in 3 seconds...")
    batch_response = client.batches.retrieve(batch_response.id)

if batch_response.status == "completed":
    print("Batch job completed successfully!")
    print(f"Request counts: {batch_response.request_counts}")

    result_file_id = batch_response.output_file_id
    file_response = client.files.content(result_file_id)
    result_content = file_response.read().decode("utf-8")

    results = [
        json.loads(line) for line in result_content.split("\n") if line.strip() != ""
    ]

    for result in results:
        print_highlight(f"Request {result['custom_id']}:")
        print_highlight(f"Response: {result['response']}")

    print_highlight("Cleaning up files...")
    # Only delete the result file ID since file_response is just content
    client.files.delete(result_file_id)
else:
    print_highlight(f"Batch job failed with status: {batch_response.status}")
    if hasattr(batch_response, "errors"):
        print_highlight(f"Errors: {batch_response.errors}")

It takes a while to complete the batch job. You can use these two APIs to retrieve the batch job status or cancel the batch job.

1. batches/{batch_id}: Retrieve the batch job status.
2. batches/{batch_id}/cancel: Cancel the batch job.

Here is an example to check the batch job status.

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import json
import time
from openai import OpenAI

client = OpenAI(base_url=f"http://127.0.0.1:{port}/v1", api_key="None")

requests = []
for i in range(20):
    requests.append(
        {
            "custom_id": f"request-{i}",
            "method": "POST",
            "url": "/chat/completions",
            "body": {
                "model": "meta-llama/Meta-Llama-3.1-8B-Instruct",
                "messages": [
                    {
                        "role": "system",
                        "content": f"{i}: You are a helpful AI assistant",
                    },
                    {
                        "role": "user",
                        "content": "Write a detailed story about topic. Make it very long.",
                    },
                ],
                "max_tokens": 64,
            },
        }
    )

input_file_path = "batch_requests.jsonl"
with open(input_file_path, "w") as f:
    for req in requests:
        f.write(json.dumps(req) + "\n")

with open(input_file_path, "rb") as f:
    uploaded_file = client.files.create(file=f, purpose="batch")

batch_job = client.batches.create(
    input_file_id=uploaded_file.id,
    endpoint="/v1/chat/completions",
    completion_window="24h",
)

print_highlight(f"Created batch job with ID: {batch_job.id}")
print_highlight(f"Initial status: {batch_job.status}")

time.sleep(10)

max_checks = 5
for i in range(max_checks):
    batch_details = client.batches.retrieve(batch_id=batch_job.id)

    print_highlight(
        f"Batch job details (check {i+1} / {max_checks}) // ID: {batch_details.id} // Status: {batch_details.status} // Created at: {batch_details.created_at} // Input file ID: {batch_details.input_file_id} // Output file ID: {batch_details.output_file_id}"
    )
    print_highlight(
        f"<strong>Request counts: Total: {batch_details.request_counts.total} // Completed: {batch_details.request_counts.completed} // Failed: {batch_details.request_counts.failed}</strong>"
    )

    time.sleep(3)

Here is an example to cancel a batch job.

In [ ]:

import json
import time
from openai import OpenAI
import os

client = OpenAI(base_url=f"http://127.0.0.1:{port}/v1", api_key="None")

requests = []
for i in range(5000):
    requests.append(
        {
            "custom_id": f"request-{i}",
            "method": "POST",
            "url": "/chat/completions",
            "body": {
                "model": "meta-llama/Meta-Llama-3.1-8B-Instruct",
                "messages": [
                    {
                        "role": "system",
                        "content": f"{i}: You are a helpful AI assistant",
                    },
                    {
                        "role": "user",
                        "content": "Write a detailed story about topic. Make it very long.",
                    },
                ],
                "max_tokens": 128,
            },
        }
    )

input_file_path = "batch_requests.jsonl"
with open(input_file_path, "w") as f:
    for req in requests:
        f.write(json.dumps(req) + "\n")

with open(input_file_path, "rb") as f:
    uploaded_file = client.files.create(file=f, purpose="batch")

batch_job = client.batches.create(
    input_file_id=uploaded_file.id,
    endpoint="/v1/chat/completions",
    completion_window="24h",
)

print_highlight(f"Created batch job with ID: {batch_job.id}")
print_highlight(f"Initial status: {batch_job.status}")

time.sleep(10)

try:
    cancelled_job = client.batches.cancel(batch_id=batch_job.id)
    print_highlight(f"Cancellation initiated. Status: {cancelled_job.status}")
    assert cancelled_job.status == "cancelling"

    # Monitor the cancellation process
    while cancelled_job.status not in ["failed", "cancelled"]:
        time.sleep(3)
        cancelled_job = client.batches.retrieve(batch_job.id)
        print_highlight(f"Current status: {cancelled_job.status}")

    # Verify final status
    assert cancelled_job.status == "cancelled"
    print_highlight("Batch job successfully cancelled")

except Exception as e:
    print_highlight(f"Error during cancellation: {e}")
    raise e

finally:
    try:
        del_response = client.files.delete(uploaded_file.id)
        if del_response.deleted:
            print_highlight("Successfully cleaned up input file")
        if os.path.exists(input_file_path):
            os.remove(input_file_path)
            print_highlight("Successfully deleted local batch_requests.jsonl file")
    except Exception as e:
        print_highlight(f"Error cleaning up: {e}")
        raise e

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terminate_process(server_process)