Chat Completions API | Unified LLM Interface

API Endpoint

POST https://api2.laozhang.ai/v1/chat/completions

Full compatibility with OpenAI official formatLaozhang API is fully compatible with OpenAI official interface format, you can directly replace https://api.openai.com/v1 with https://api2.laozhang.ai/v1 to use.

Request Parameters

Required Parameters

string

required

Model name to useSupported models:

OpenAI Series: gpt-4o, gpt-4o-mini, gpt-4-turbo, gpt-3.5-turbo, etc.
Claude Series: claude-3-5-sonnet, claude-3-opus, claude-3-haiku, etc.
Gemini Series: gemini-1.5-pro, gemini-1.5-flash, gemini-2.0-flash-exp, etc.
Chinese Models: deepseek-chat, qwen-max, glm-4-flash, yi-lightning, etc.

For complete model list, see API Reference - Models

array

required

Conversation message array, each message contains role and content

[
  {
    "role": "system",
    "content": "You are a helpful assistant"
  },
  {
    "role": "user", 
    "content": "Hello!"
  }
]

Role Descriptions:

system: System prompt, defines AI assistant behavior
user: User message
assistant: AI assistant’s previous response

Optional Parameters

number

default:"1"

Randomness of generated results, range 0-2

0: Deterministic, minimal randomness (recommended for translation, summarization, etc.)
0.7: Balanced, suitable for most scenarios
1.5-2: High creativity (recommended for creative writing, brainstorming, etc.)

integer

Maximum number of tokens to generate

If not set, model will use its default limit. If response is truncated, try increasing this value.

Recommended Values:

Short responses: 500-1000
Medium responses: 2000-4000
Long responses: 8000+

boolean

default:"false"

Whether to use stream output

false: Wait for complete response
true: Receive response in chunks (better user experience)

number

default:"1"

Nucleus sampling parameter, range 0-1Controls diversity of output. Generally use either temperature or top_p, not both simultaneously.

number

default:"0"

Frequency penalty, range -2.0 to 2.0Positive values reduce repetition of already appearing content.

number

default:"0"

Presence penalty, range -2.0 to 2.0Positive values encourage discussion of new topics.

string | array

Stop sequences, generation stops when these strings are encounteredCan be a single string or array of up to 4 strings.

string

End user unique identifier for abuse detectionRecommended for multi-user scenarios.

Message Format

Basic Text Message

{
  "role": "user",
  "content": "Please introduce yourself"
}

Multimodal Message (Image Understanding)

Image URL
Base64 Image

{
  "role": "user",
  "content": [
    {
      "type": "text",
      "text": "What's in this image?"
    },
    {
      "type": "image_url",
      "image_url": {
        "url": "https://example.com/image.jpg"
      }
    }
  ]
}

{
  "role": "user",
  "content": [
    {
      "type": "text",
      "text": "Please analyze this image"
    },
    {
      "type": "image_url",
      "image_url": {
        "url": "data:image/jpeg;base64,/9j/4AAQSkZJRg..."
      }
    }
  ]
}

Multimodal ModelsSupport image understanding:

OpenAI: gpt-4o, gpt-4o-mini, gpt-4-turbo
Claude: claude-3-5-sonnet, claude-3-opus, claude-3-sonnet, claude-3-haiku
Gemini: gemini-1.5-pro, gemini-1.5-flash, gemini-2.0-flash-exp

Request Examples

cURL

curl https://api2.laozhang.ai/v1/chat/completions \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -d '{
    "model": "gpt-4o-mini",
    "messages": [
      {
        "role": "system",
        "content": "You are a helpful assistant"
      },
      {
        "role": "user",
        "content": "What is the capital of France?"
      }
    ]
  }'

curl https://api2.laozhang.ai/v1/chat/completions \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -d '{
    "model": "gpt-4o-mini",
    "messages": [
      {
        "role": "user",
        "content": "Tell me a story"
      }
    ],
    "stream": true
  }'

curl https://api2.laozhang.ai/v1/chat/completions \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -d '{
    "model": "gpt-4o",
    "messages": [
      {
        "role": "user",
        "content": [
          {
            "type": "text",
            "text": "What is in this image?"
          },
          {
            "type": "image_url",
            "image_url": {
              "url": "https://example.com/image.jpg"
            }
          }
        ]
      }
    ]
  }'

Node.js

import OpenAI from 'openai';

const openai = new OpenAI({
  apiKey: 'YOUR_API_KEY',
  baseURL: 'https://api2.laozhang.ai/v1'
});

// Basic dialogue
const completion = await openai.chat.completions.create({
  model: 'gpt-4o-mini',
  messages: [
    { role: 'system', content: 'You are a helpful assistant' },
    { role: 'user', content: 'What is the capital of France?' }
  ]
});

console.log(completion.choices[0].message.content);

// Stream output
const stream = await openai.chat.completions.create({
  model: 'gpt-4o-mini',
  messages: [
    { role: 'user', content: 'Tell me a story' }
  ],
  stream: true
});

for await (const chunk of stream) {
  process.stdout.write(chunk.choices[0]?.delta?.content || '');
}

import axios from 'axios';

const response = await axios.post(
  'https://api2.laozhang.ai/v1/chat/completions',
  {
    model: 'gpt-4o-mini',
    messages: [
      { role: 'user', content: 'Hello!' }
    ]
  },
  {
    headers: {
      'Content-Type': 'application/json',
      'Authorization': 'Bearer YOUR_API_KEY'
    }
  }
);

console.log(response.data.choices[0].message.content);

Python

from openai import OpenAI

client = OpenAI(
    api_key="YOUR_API_KEY",
    base_url="https://api2.laozhang.ai/v1"
)

# Basic dialogue
completion = client.chat.completions.create(
    model="gpt-4o-mini",
    messages=[
        {"role": "system", "content": "You are a helpful assistant"},
        {"role": "user", "content": "What is the capital of France?"}
    ]
)

print(completion.choices[0].message.content)

# Stream output
stream = client.chat.completions.create(
    model="gpt-4o-mini",
    messages=[
        {"role": "user", "content": "Tell me a story"}
    ],
    stream=True
)

for chunk in stream:
    if chunk.choices[0].delta.content:
        print(chunk.choices[0].delta.content, end="")

# Image understanding
completion = client.chat.completions.create(
    model="gpt-4o",
    messages=[
        {
            "role": "user",
            "content": [
                {"type": "text", "text": "What's in this image?"},
                {
                    "type": "image_url",
                    "image_url": {
                        "url": "https://example.com/image.jpg"
                    }
                }
            ]
        }
    ]
)

print(completion.choices[0].message.content)

import requests

url = "https://api2.laozhang.ai/v1/chat/completions"
headers = {
    "Content-Type": "application/json",
    "Authorization": "Bearer YOUR_API_KEY"
}
data = {
    "model": "gpt-4o-mini",
    "messages": [
        {"role": "user", "content": "Hello!"}
    ]
}

response = requests.post(url, headers=headers, json=data)
result = response.json()

print(result['choices'][0]['message']['content'])

Go

package main

import (
    "context"
    "fmt"
    "github.com/sashabaranov/go-openai"
)

func main() {
    config := openai.DefaultConfig("YOUR_API_KEY")
    config.BaseURL = "https://api2.laozhang.ai/v1"
    client := openai.NewClientWithConfig(config)

    resp, err := client.CreateChatCompletion(
        context.Background(),
        openai.ChatCompletionRequest{
            Model: "gpt-4o-mini",
            Messages: []openai.ChatCompletionMessage{
                {
                    Role:    openai.ChatMessageRoleSystem,
                    Content: "You are a helpful assistant",
                },
                {
                    Role:    openai.ChatMessageRoleUser,
                    Content: "What is the capital of France?",
                },
            },
        },
    )

    if err != nil {
        fmt.Printf("Error: %v\n", err)
        return
    }

    fmt.Println(resp.Choices[0].Message.Content)
}

Response Format

Standard Response

{
  "id": "chatcmpl-abc123",
  "object": "chat.completion",
  "created": 1699999999,
  "model": "gpt-4o-mini",
  "choices": [
    {
      "index": 0,
      "message": {
        "role": "assistant",
        "content": "The capital of France is Paris."
      },
      "finish_reason": "stop"
    }
  ],
  "usage": {
    "prompt_tokens": 20,
    "completion_tokens": 10,
    "total_tokens": 30
  }
}

Stream Response

Each chunk format:

{
  "id": "chatcmpl-abc123",
  "object": "chat.completion.chunk",
  "created": 1699999999,
  "model": "gpt-4o-mini",
  "choices": [
    {
      "index": 0,
      "delta": {
        "content": "Paris"
      },
      "finish_reason": null
    }
  ]
}

Last chunk (finish_reason not null):

{
  "id": "chatcmpl-abc123",
  "object": "chat.completion.chunk",
  "created": 1699999999,
  "model": "gpt-4o-mini",
  "choices": [
    {
      "index": 0,
      "delta": {},
      "finish_reason": "stop"
    }
  ],
  "usage": {
    "prompt_tokens": 20,
    "completion_tokens": 10,
    "total_tokens": 30
  }
}

Response Field Descriptions

string

Unique request identifier

string

Object type:

chat.completion: Standard response
chat.completion.chunk: Stream response chunk

integer

Creation timestamp (Unix timestamp)

string

Model name used

array

Generated results array, typically containing one result

integer

Result index

object

Message object (standard response)

string

Role, always assistant

string

Generated content

object

Incremental content (stream response)

string

This chunk’s content

string

Completion reason:

stop: Natural completion
length: Reached max_tokens limit
content_filter: Content filtered by policy
null: Not yet finished (stream output)

object

Token usage statistics

integer

Input tokens

integer

Output tokens

integer

Total tokens

Special Usage

GPT-4o Vision

from openai import OpenAI

client = OpenAI(
    api_key="YOUR_API_KEY",
    base_url="https://api2.laozhang.ai/v1"
)

completion = client.chat.completions.create(
    model="gpt-4o",
    messages=[
        {
            "role": "user",
            "content": [
                {"type": "text", "text": "Please describe this image in detail"},
                {
                    "type": "image_url",
                    "image_url": {
                        "url": "https://example.com/image.jpg",
                        # Optional: control image quality
                        # "detail": "high"  # or "low"
                    }
                }
            ]
        }
    ],
    max_tokens=1000
)

print(completion.choices[0].message.content)

Multiple ImagesGPT-4o supports analyzing multiple images simultaneously, just add multiple image_url objects to the content array.

Claude Native Format

Claude models also support native format:

import anthropic

client = anthropic.Anthropic(
    api_key="YOUR_API_KEY",
    base_url="https://api2.laozhang.ai/v1"
)

message = client.messages.create(
    model="claude-3-5-sonnet-20241022",
    max_tokens=1024,
    messages=[
        {"role": "user", "content": "Hello, Claude"}
    ]
)

print(message.content[0].text)

O1 Series Special Parameters

O1 series models (o1-preview, o1-mini) have parameter limitations:

O1 Series Limitations

Do not support system role messages
Do not support stream output (stream must be false)
Do not support temperature, top_p, presence_penalty, frequency_penalty parameters
max_tokens defaults to model’s maximum value

Correct usage:

completion = client.chat.completions.create(
    model="o1-mini",
    messages=[
        {
            "role": "user",
            "content": "Please solve this math problem: ..."
        }
    ]
)

Usage Tips

Multi-turn Dialogue

Implement multi-turn dialogue by passing context:

messages = [
    {"role": "system", "content": "You are a helpful assistant"},
]

# First round
messages.append({"role": "user", "content": "What's the weather in Beijing?"})
response = client.chat.completions.create(
    model="gpt-4o-mini",
    messages=messages
)
messages.append({"role": "assistant", "content": response.choices[0].message.content})

# Second round
messages.append({"role": "user", "content": "What about Shanghai?"})
response = client.chat.completions.create(
    model="gpt-4o-mini",
    messages=messages
)

JSON Output

Get structured JSON output:

completion = client.chat.completions.create(
    model="gpt-4o-mini",
    messages=[
        {
            "role": "system",
            "content": "You are a helpful assistant. Always output in JSON format."
        },
        {
            "role": "user",
            "content": "Extract structured fields from this support ticket: ticket A-1024, priority high, department engineering"
        }
    ],
    response_format={"type": "json_object"}  # Force JSON output
)

import json
result = json.loads(completion.choices[0].message.content)
print(result)

JSON Mode SupportCurrently supports JSON mode models:

GPT-4o series
GPT-4-turbo series
GPT-3.5-turbo-1106 and later versions

Billing

Billing is based on actual token usage: Total Cost = (Input Tokens × Input Price + Output Tokens × Output Price)

Save Costs

Choose appropriate models: Most scenarios don’t require GPT-4o, gpt-4o-mini or gpt-3.5-turbo are sufficient
Control context length: Only pass necessary historical messages
Set max_tokens: Avoid unnecessarily long output
Use mini series models: For simple tasks, mini models are lightweight choices

Model Price Reference

Model	Input Price	Output Price	Features
gpt-4o-mini	$0.15/1M tokens	$0.60/1M tokens	Cost-effective, supports image understanding
gpt-4o	$2.5/1M tokens	$10/1M tokens	Strongest capabilities, supports multimodal
claude-3-5-sonnet	$3/1M tokens	$15/1M tokens	Excellent reasoning, supports image understanding
gemini-1.5-flash	$0.075/1M tokens	$0.3/1M tokens	Fastest speed, long context

For complete pricing, see Pricing

Error Handling

Common error codes:

Error Code	Meaning	Solution
401	API Key invalid or missing	Check if API Key is correct
429	Request rate limit exceeded	Slow down request frequency or upgrade plan
500	Server internal error	Retry request or contact support
400	Request parameter error	Check if request parameters conform to API documentation

Error response example:

{
  "error": {
    "message": "Invalid API key provided",
    "type": "invalid_request_error",
    "code": "invalid_api_key"
  }
}

Best Practices

Use Appropriate Temperature
- Translation, summarization, Q&A: temperature=0
- General dialogue: temperature=0.7
- Creative writing: temperature=1.0-1.5
Control Context Length
- Only pass necessary historical messages
- Regularly clean up irrelevant context
- Long documents can be processed in segments
Choose Right Model
- Simple tasks: gpt-4o-mini, gpt-3.5-turbo
- Reasoning tasks: claude-3-5-sonnet, gpt-4o
- Cost-sensitive: gemini-1.5-flash
Error Retry
- Implement exponential backoff retry mechanism
- Catch and handle different error types
- Set reasonable timeout
Stream Output
- Better user experience for long responses
- Reduce perceived latency
- Can implement typewriter effect

Models API - Get complete available model list
Images API - Image generation and editing
OpenAI Models Guide - Detailed GPT-4o usage
Claude Models Guide - Detailed Claude usage
Gemini Models Guide - Detailed Gemini usage

Core APIs

Model Guides

Chat Completions API | Unified LLM Interface | LaoZhang API

API Endpoint

Request Parameters

Required Parameters

Optional Parameters

Message Format

Basic Text Message

Multimodal Message (Image Understanding)

Request Examples

cURL

Node.js

Python

Go

Response Format

Standard Response

Stream Response

Response Field Descriptions

Special Usage

GPT-4o Vision

Claude Native Format

O1 Series Special Parameters

Usage Tips

Multi-turn Dialogue

JSON Output

Billing

Model Price Reference

Error Handling

Best Practices

​API Endpoint

​Request Parameters

​Required Parameters

​Optional Parameters

​Message Format

​Basic Text Message

​Multimodal Message (Image Understanding)

​Request Examples

​cURL

​Node.js

​Python

​Go

​Response Format

​Standard Response

​Stream Response

​Response Field Descriptions

​Special Usage

​GPT-4o Vision

​Claude Native Format

​O1 Series Special Parameters

​Usage Tips

​Multi-turn Dialogue

​JSON Output

​Billing

​Model Price Reference

​Error Handling

​Best Practices

​Related Resources

API Endpoint

Request Parameters

Required Parameters

Optional Parameters

Message Format

Basic Text Message

Multimodal Message (Image Understanding)

Request Examples

cURL

Node.js

Python

Go

Response Format

Standard Response

Stream Response

Response Field Descriptions

Special Usage

GPT-4o Vision

Claude Native Format

O1 Series Special Parameters

Usage Tips

Multi-turn Dialogue

JSON Output

Billing

Model Price Reference

Error Handling

Best Practices

Related Resources