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sglang
GitHub高性能LLM推理框架，核心特性为RadixAttention前缀缓存。适用于结构化输出、智能体工作流及多轮对话场景，相比vLLM在共享上下文下速度提升5倍。
Trigger Scenarios
需要JSON或正则约束的输出
构建带有重复前缀的智能体
多轮对话共享上下文加速
需要比vLLM更快的推理速度
Install
npx skills add synthetic-sciences/openscience --skill sglang -g -y
SKILL.md
Frontmatter
{
"name": "sglang",
"tags": [
"Inference Serving",
"SGLang",
"Structured Generation",
"RadixAttention",
"Prefix Caching",
"Constrained Decoding",
"Agents",
"JSON Output",
"Fast Inference",
"Production Scale"
],
"author": "Synthetic Sciences",
"license": "MIT",
"version": "1.0.0",
"category": "ml-inference",
"description": "Fast structured generation and serving for LLMs with RadixAttention prefix caching. Use for JSON\/regex outputs, constrained decoding, agentic workflows with tool calls, or when you need 5× faster inference than vLLM with prefix sharing. Powers 300,000+ GPUs at xAI, AMD, NVIDIA, and LinkedIn.",
"dependencies": [
"sglang",
"torch",
"transformers"
]
}
SGLang
High-performance serving framework for LLMs and VLMs with RadixAttention for automatic prefix caching.
When to use SGLang
Use SGLang when:
- Need structured outputs (JSON, regex, grammar)
- Building agents with repeated prefixes (system prompts, tools)
- Agentic workflows with function calling
- Multi-turn conversations with shared context
- Need faster JSON decoding (3× vs standard)
Use vLLM instead when:
- Simple text generation without structure
- Don't need prefix caching
- Want mature, widely-tested production system
Use TensorRT-LLM instead when:
- Maximum single-request latency (no batching needed)
- NVIDIA-only deployment
- Need FP8/INT4 quantization on H100
Quick start
Installation
# pip install (recommended)
pip install "sglang[all]"
# With FlashInfer (faster, CUDA 11.8/12.1)
pip install sglang[all] flashinfer -i https://flashinfer.ai/whl/cu121/torch2.4/
# From source
git clone https://github.com/sgl-project/sglang.git
cd sglang
pip install -e "python[all]"
Launch server
# Basic server (Llama 3-8B)
python -m sglang.launch_server \
--model-path meta-llama/Meta-Llama-3-8B-Instruct \
--port 30000
# With RadixAttention (automatic prefix caching)
python -m sglang.launch_server \
--model-path meta-llama/Meta-Llama-3-8B-Instruct \
--port 30000 \
--enable-radix-cache # Default: enabled
# Multi-GPU (tensor parallelism)
python -m sglang.launch_server \
--model-path meta-llama/Meta-Llama-3-70B-Instruct \
--tp 4 \
--port 30000
Basic inference
import sglang as sgl
# Set backend
sgl.set_default_backend(sgl.OpenAI("http://localhost:30000/v1"))
# Simple generation
@sgl.function
def simple_gen(s, question):
s += "Q: " + question + "\n"
s += "A:" + sgl.gen("answer", max_tokens=100)
# Run
state = simple_gen.run(question="What is the capital of France?")
print(state["answer"])
# Output: "The capital of France is Paris."
Structured JSON output
import sglang as sgl
@sgl.function
def extract_person(s, text):
s += f"Extract person information from: {text}\n"
s += "Output JSON:\n"
# Constrained JSON generation
s += sgl.gen(
"json_output",
max_tokens=200,
regex=r'\{"name": "[^"]+", "age": \d+, "occupation": "[^"]+"\}'
)
# Run
state = extract_person.run(
text="John Smith is a 35-year-old software engineer."
)
print(state["json_output"])
# Output: {"name": "John Smith", "age": 35, "occupation": "software engineer"}
RadixAttention (Key Innovation)
What it does: Automatically caches and reuses common prefixes across requests.
Performance:
- 5× faster for agentic workloads with shared system prompts
- 10× faster for few-shot prompting with repeated examples
- Zero configuration - works automatically
How it works:
- Builds radix tree of all processed tokens
- Automatically detects shared prefixes
- Reuses KV cache for matching prefixes
- Only computes new tokens
Example (Agent with system prompt):
Request 1: [SYSTEM_PROMPT] + "What's the weather?"
→ Computes full prompt (1000 tokens)
Request 2: [SAME_SYSTEM_PROMPT] + "Book a flight"
→ Reuses system prompt KV cache (998 tokens)
→ Only computes 2 new tokens
→ 5× faster!
Structured generation patterns
JSON with schema
@sgl.function
def structured_extraction(s, article):
s += f"Article: {article}\n\n"
s += "Extract key information as JSON:\n"
# JSON schema constraint
schema = {
"type": "object",
"properties": {
"title": {"type": "string"},
"author": {"type": "string"},
"summary": {"type": "string"},
"sentiment": {"type": "string", "enum": ["positive", "negative", "neutral"]}
},
"required": ["title", "author", "summary", "sentiment"]
}
s += sgl.gen("info", max_tokens=300, json_schema=schema)
state = structured_extraction.run(article="...")
print(state["info"])
# Output: Valid JSON matching schema
Regex-constrained generation
@sgl.function
def extract_email(s, text):
s += f"Extract email from: {text}\n"
s += "Email: "
# Email regex pattern
s += sgl.gen(
"email",
max_tokens=50,
regex=r'[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}'
)
state = extract_email.run(text="Contact john.doe@example.com for details")
print(state["email"])
# Output: "john.doe@example.com"
Grammar-based generation
@sgl.function
def generate_code(s, description):
s += f"Generate Python code for: {description}\n"
s += "```python\n"
# EBNF grammar for Python
python_grammar = """
?start: function_def
function_def: "def" NAME "(" [parameters] "):" suite
parameters: parameter ("," parameter)*
parameter: NAME
suite: simple_stmt | NEWLINE INDENT stmt+ DEDENT
"""
s += sgl.gen("code", max_tokens=200, grammar=python_grammar)
s += "\n```"
Agent workflows with function calling
import sglang as sgl
# Define tools
tools = [
{
"name": "get_weather",
"description": "Get weather for a location",
"parameters": {
"type": "object",
"properties": {
"location": {"type": "string"}
}
}
},
{
"name": "book_flight",
"description": "Book a flight",
"parameters": {
"type": "object",
"properties": {
"from": {"type": "string"},
"to": {"type": "string"},
"date": {"type": "string"}
}
}
}
]
@sgl.function
def agent_workflow(s, user_query, tools):
# System prompt (cached with RadixAttention)
s += "You are a helpful assistant with access to tools.\n"
s += f"Available tools: {tools}\n\n"
# User query
s += f"User: {user_query}\n"
s += "Assistant: "
# Generate with function calling
s += sgl.gen(
"response",
max_tokens=200,
tools=tools, # SGLang handles tool call format
stop=["User:", "\n\n"]
)
# Multiple queries reuse system prompt
state1 = agent_workflow.run(
user_query="What's the weather in NYC?",
tools=tools
)
# First call: Computes full system prompt
state2 = agent_workflow.run(
user_query="Book a flight to LA",
tools=tools
)
# Second call: Reuses system prompt (5× faster)
Performance benchmarks
RadixAttention speedup
Few-shot prompting (10 examples in prompt):
- vLLM: 2.5 sec/request
- SGLang: 0.25 sec/request (10× faster)
- Throughput: 4× higher
Agent workflows (1000-token system prompt):
- vLLM: 1.8 sec/request
- SGLang: 0.35 sec/request (5× faster)
JSON decoding:
- Standard: 45 tok/s
- SGLang: 135 tok/s (3× faster)
Throughput (Llama 3-8B, A100)
| Workload | vLLM | SGLang | Speedup |
|---|---|---|---|
| Simple generation | 2500 tok/s | 2800 tok/s | 1.12× |
| Few-shot (10 examples) | 500 tok/s | 5000 tok/s | 10× |
| Agent (tool calls) | 800 tok/s | 4000 tok/s | 5× |
| JSON output | 600 tok/s | 2400 tok/s | 4× |
Multi-turn conversations
@sgl.function
def multi_turn_chat(s, history, new_message):
# System prompt (always cached)
s += "You are a helpful AI assistant.\n\n"
# Conversation history (cached as it grows)
for msg in history:
s += f"{msg['role']}: {msg['content']}\n"
# New user message (only new part)
s += f"User: {new_message}\n"
s += "Assistant: "
s += sgl.gen("response", max_tokens=200)
# Turn 1
history = []
state = multi_turn_chat.run(history=history, new_message="Hi there!")
history.append({"role": "User", "content": "Hi there!"})
history.append({"role": "Assistant", "content": state["response"]})
# Turn 2 (reuses Turn 1 KV cache)
state = multi_turn_chat.run(history=history, new_message="What's 2+2?")
# Only computes new message (much faster!)
# Turn 3 (reuses Turn 1 + Turn 2 KV cache)
state = multi_turn_chat.run(history=history, new_message="Tell me a joke")
# Progressively faster as history grows
Advanced features
Speculative decoding
# Launch with draft model (2-3× faster)
python -m sglang.launch_server \
--model-path meta-llama/Meta-Llama-3-70B-Instruct \
--speculative-model meta-llama/Meta-Llama-3-8B-Instruct \
--speculative-num-steps 5
Multi-modal (vision models)
@sgl.function
def describe_image(s, image_path):
s += sgl.image(image_path)
s += "Describe this image in detail: "
s += sgl.gen("description", max_tokens=200)
state = describe_image.run(image_path="photo.jpg")
print(state["description"])
Batching and parallel requests
# Automatic batching (continuous batching)
states = sgl.run_batch(
[
simple_gen.bind(question="What is AI?"),
simple_gen.bind(question="What is ML?"),
simple_gen.bind(question="What is DL?"),
]
)
# All 3 processed in single batch (efficient)
OpenAI-compatible API
# Start server with OpenAI API
python -m sglang.launch_server \
--model-path meta-llama/Meta-Llama-3-8B-Instruct \
--port 30000
# Use with OpenAI client
curl http://localhost:30000/v1/chat/completions \
-H "Content-Type: application/json" \
-d '{
"model": "default",
"messages": [
{"role": "system", "content": "You are helpful"},
{"role": "user", "content": "Hello"}
],
"temperature": 0.7,
"max_tokens": 100
}'
# Works with OpenAI Python SDK
from openai import OpenAI
client = OpenAI(base_url="http://localhost:30000/v1", api_key="EMPTY")
response = client.chat.completions.create(
model="default",
messages=[{"role": "user", "content": "Hello"}]
)
Supported models
Text models:
- Llama 2, Llama 3, Llama 3.1, Llama 3.2
- Mistral, Mixtral
- Qwen, Qwen2, QwQ
- DeepSeek-V2, DeepSeek-V3
- Gemma, Phi-3
Vision models:
- LLaVA, LLaVA-OneVision
- Phi-3-Vision
- Qwen2-VL
100+ models from HuggingFace
Hardware support
NVIDIA: A100, H100, L4, T4 (CUDA 11.8+) AMD: MI300, MI250 (ROCm 6.0+) Intel: Xeon with GPU (coming soon) Apple: M1/M2/M3 via MPS (experimental)
References
- Structured Generation Guide - JSON schemas, regex, grammars, validation
- RadixAttention Deep Dive - How it works, optimization, benchmarks
- Production Deployment - Multi-GPU, monitoring, autoscaling
Known Conflicts
- Do not install alongside
vllmin the same environment. Both bind to full GPU memory and cannot coexist in the same process. Use separate environments or containers.
Resources
- GitHub: https://github.com/sgl-project/sglang
- Docs: https://sgl-project.github.io/
- Paper: RadixAttention (arXiv:2312.07104)
- Discord: https://discord.gg/sglang
Version History
- e9844a4 Current 2026-07-11 17:28
Dependencies
-
required
sglang -
required
torch - required transformers
