flashinfer-python 0.6.4
FlashInfer: Kernel Library for LLM Serving
Requires Python: <4.0,>=3.10

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High-Performance GPU Kernels for Inference
</h1>

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**FlashInfer** is a library and kernel generator for inference that delivers state-of-the-art performance across diverse GPU architectures. It provides unified APIs for attention, GEMM, and MoE operations with multiple backend implementations including FlashAttention-2/3, cuDNN, CUTLASS, and TensorRT-LLM.

## Why FlashInfer?

- **State-of-the-art Performance**: Optimized kernels for prefill, decode, and mixed batching scenarios
- **Multiple Backends**: Automatically selects the best backend for your hardware and workload
- **Modern Architecture Support**: Support for SM75 (Turing) and later (through Blackwell)
- **Low-Precision Compute**: FP8 and FP4 quantization for attention, GEMM, and MoE operations
- **Production-Ready**: CUDAGraph and torch.compile compatible for low-latency serving

## Core Features

### Attention Kernels
- **Paged and Ragged KV-Cache**: Efficient memory management for dynamic batch serving
- **Decode, Prefill, and Append**: Optimized kernels for all attention phases
- **MLA Attention**: Native support for DeepSeek's Multi-Latent Attention
- **Cascade Attention**: Memory-efficient hierarchical KV-Cache for shared prefixes
- **Sparse Attention**: Block-sparse and variable block-sparse patterns
- **POD-Attention**: Fused prefill+decode for mixed batching

### GEMM & Linear Operations
- **FP8 GEMM**: Per-tensor and groupwise scaling
- **FP4 GEMM**: NVFP4 and MXFP4 matrix multiplication for Blackwell GPUs
- **Grouped GEMM**: Efficient batched matrix operations for LoRA and multi-expert routing

### Mixture of Experts (MoE)
- **Fused MoE Kernels**
- **Multiple Routing Methods**: DeepSeek-V3, Llama-4, and standard top-k routing
- **Quantized MoE**: FP8 and FP4 expert weights with block-wise scaling

### Sampling & Decoding
- **Sorting-Free Sampling**: Efficient Top-K, Top-P, and Min-P without sorting
- **Speculative Decoding**: Chain speculative sampling support

### Communication
- **AllReduce**: Custom implementations
- **Multi-Node NVLink**: MNNVL support for multi-node inference
- **NVSHMEM Integration**: For distributed memory operations

### Other Operators
- **RoPE**: LLaMA-style rotary position embeddings (including LLaMA 3.1)
- **Normalization**: RMSNorm, LayerNorm, Gemma-style fused operations
- **Activations**: SiLU, GELU with fused gating

## GPU Support

| Architecture | Compute Capability | Example GPUs |
|--------------|-------------------|------|
| Turing | SM 7.5 | T4, RTX 20 series |
| Ampere | SM 8.0, 8.6 | A100, A10, RTX 30 series |
| Ada Lovelace | SM 8.9 | L4, L40, RTX 40 series |
| Hopper | SM 9.0 | H100, H200 |
| Blackwell | SM 10.0, 10.3 | B200, B300 |
| Blackwell | SM 12.0, 12.1 | RTX 50 series, DGX Spark, Jetson Thor |

> **Note:** Not all features are supported across all compute capabilities.

## News

Latest: [![GitHub Release](https://img.shields.io/github/v/release/flashinfer-ai/flashinfer)](https://github.com/flashinfer-ai/flashinfer/releases/latest)

Notable updates:
- [2025-10-08] Blackwell support added in [v0.4.0](https://github.com/flashinfer-ai/flashinfer/releases/tag/v0.4.0)
- [2025-03-10] [Blog Post](https://flashinfer.ai/2025/03/10/sampling.html) Sorting-Free GPU Kernels for LLM Sampling, which explains the design of sampling kernels in FlashInfer.

## Getting Started

### Installation

**Quickstart:**

```bash
pip install flashinfer-python
```

**Package Options:**

- **flashinfer-python**: Core package that compiles/downloads kernels on first use
- **flashinfer-cubin**: Pre-compiled kernel binaries for all supported GPU architectures
- **flashinfer-jit-cache**: Pre-built kernel cache for specific CUDA versions

**For faster initialization and offline usage**, install the optional packages to have most kernels pre-compiled:

```bash
pip install flashinfer-python flashinfer-cubin
# JIT cache (replace cu129 with your CUDA version)
pip install flashinfer-jit-cache --index-url https://flashinfer.ai/whl/cu129
```

### Verify Installation

```bash
flashinfer show-config
```

### Basic Usage

```python
import torch
import flashinfer

# Single decode attention
q = torch.randn(32, 128, device="cuda", dtype=torch.float16)  # [num_qo_heads, head_dim]
k = torch.randn(2048, 32, 128, device="cuda", dtype=torch.float16)  # [kv_len, num_kv_heads, head_dim]
v = torch.randn(2048, 32, 128, device="cuda", dtype=torch.float16)

output = flashinfer.single_decode_with_kv_cache(q, k, v)
```

See [documentation](https://docs.flashinfer.ai/) for comprehensive API reference and tutorials.

### Install from Source

```bash
git clone https://github.com/flashinfer-ai/flashinfer.git --recursive
cd flashinfer
python -m pip install -v .
```

**For development**, install in editable mode:

```bash
python -m pip install --no-build-isolation -e . -v
```

Build optional packages:

```bash
# flashinfer-cubin
cd flashinfer-cubin
python -m build --no-isolation --wheel
python -m pip install dist/*.whl
```

```bash
# flashinfer-jit-cache (customize for your target GPUs)
export FLASHINFER_CUDA_ARCH_LIST="7.5 8.0 8.9 9.0a 10.0a 10.3a 11.0a 12.0f"
cd flashinfer-jit-cache
python -m build --no-isolation --wheel
python -m pip install dist/*.whl
```

For more details, see the [Install from Source documentation](https://docs.flashinfer.ai/installation.html#install-from-source).

### Nightly Builds

```bash
pip install -U --pre flashinfer-python --index-url https://flashinfer.ai/whl/nightly/ --no-deps
pip install flashinfer-python  # Install dependencies from PyPI
pip install -U --pre flashinfer-cubin --index-url https://flashinfer.ai/whl/nightly/
# JIT cache (replace cu129 with your CUDA version)
pip install -U --pre flashinfer-jit-cache --index-url https://flashinfer.ai/whl/nightly/cu129
```

### CLI Tools

FlashInfer provides several CLI commands for configuration, module management, and development:

```bash
# Verify installation and view configuration
flashinfer show-config

# List and inspect modules
flashinfer list-modules
flashinfer module-status

# Manage artifacts and cache
flashinfer download-cubin
flashinfer clear-cache

# For developers: generate compile_commands.json for IDE integration
flashinfer export-compile-commands [output_path]
```

For complete documentation, see the [CLI reference](https://docs.flashinfer.ai/cli.html).

## API Logging

FlashInfer provides comprehensive API logging for debugging. Enable it using environment variables:

```bash
# Enable logging (levels: 0=off (default), 1=basic, 3=detailed, 5=statistics)
export FLASHINFER_LOGLEVEL=3

# Set log destination (stdout (default), stderr, or file path)
export FLASHINFER_LOGDEST=stdout
```

For detailed information about logging levels, configuration, and advanced features, see [Logging](https://docs.flashinfer.ai/logging.html) in our documentation.

## Custom Attention Variants

Users can customize their own attention variants with additional parameters. For more details, refer to our [JIT examples](https://github.com/flashinfer-ai/flashinfer/blob/main/tests/utils/test_jit_example.py).

## CUDA Support

**Supported CUDA Versions:** 12.6, 12.8, 13.0, 13.1

> **Note:** FlashInfer strives to follow PyTorch's supported CUDA versions plus the latest CUDA release.

## Adoption

FlashInfer powers inference in:

- [SGLang](https://github.com/sgl-project/sglang)
- [vLLM](https://github.com/vllm-project/vllm)
- [TensorRT-LLM](https://github.com/NVIDIA/TensorRT-LLM)
- [TGI (Text Generation Inference)](https://github.com/huggingface/text-generation-inference)
- [MLC-LLM](https://github.com/mlc-ai/mlc-llm)
- [LightLLM](https://github.com/ModelTC/lightllm)
- [lorax](https://github.com/predibase/lorax)
- [ScaleLLM](https://github.com/vectorch-ai/ScaleLLM)

## Acknowledgement

FlashInfer is inspired by [FlashAttention](https://github.com/dao-AILab/flash-attention/), [vLLM](https://github.com/vllm-project/vllm), [stream-K](https://arxiv.org/abs/2301.03598), [CUTLASS](https://github.com/nvidia/cutlass), and [AITemplate](https://github.com/facebookincubator/AITemplate).

## Citation

If you find FlashInfer helpful in your project or research, please consider citing our [paper](https://arxiv.org/abs/2501.01005):

```bibtex
@article{ye2025flashinfer,
    title = {FlashInfer: Efficient and Customizable Attention Engine for LLM Inference Serving},
    author = {
      Ye, Zihao and
      Chen, Lequn and
      Lai, Ruihang and
      Lin, Wuwei and
      Zhang, Yineng and
      Wang, Stephanie and
      Chen, Tianqi and
      Kasikci, Baris and
      Grover, Vinod and
      Krishnamurthy, Arvind and
      Ceze, Luis
    },
    journal = {arXiv preprint arXiv:2501.01005},
    year = {2025},
    url = {https://arxiv.org/abs/2501.01005}
}
```