sglang

Files (4)

• SKILL.md
• deployment.md · references/
• radix-attention.md · references/
• structured-generation.md · references/

SKILL.md (first lines)

# 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

```bash
# 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

```bash
# 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

```python
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

```python
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**:
1. Builds radix tree of all processed tokens
2. Automatically detects shared prefixes
3. Reuses KV cache for matching prefixes

From Orchestra-Research/AI-Research-SKILLs, MIT.

More from Orchestra-Research/AI-Research-SKILLs