---
title: "Loading Models from Object Storage"
metatags:
    description: "Load SGLang models directly from S3, Google Cloud Storage, Azure Blob, and S3-compatible object storage with runai_streamer."
---

SGLang can load models directly from object storage without a full local download. It uses the `runai_streamer` load format to stream model weights from cloud storage, reducing startup time and local storage requirements.

## Overview

When loading models from object storage, SGLang uses a two-phase approach:

1. **Metadata Download** (once, before process launch): Configuration files and tokenizer files are downloaded to a local cache
2. **Weight Streaming** (lazy, during model loading): Model weights are streamed directly from object storage as needed

## Supported Storage Backends

1. **Amazon S3**: `s3://bucket-name/path/to/model/`
2. **Google Cloud Storage**: `gs://bucket-name/path/to/model/`
3. **Azure Blob**: `az://some-azure-container/path/`
4. **S3 compatible**: `s3://bucket-name/path/to/model/`

## Quick Start

### Basic Usage

Simply provide an object storage URI as the model path:

```bash
# S3
python -m sglang.launch_server \
  --model-path s3://my-bucket/models/llama-3-8b/ \
  --load-format runai_streamer

# Google Cloud Storage
python -m sglang.launch_server \
  --model-path gs://my-bucket/models/llama-3-8b/ \
  --load-format runai_streamer
```

**Note**: The `--load-format runai_streamer` is automatically detected when using object storage URIs, so you can omit it:

```bash
python -m sglang.launch_server \
  --model-path s3://my-bucket/models/llama-3-8b/
```

### With Tensor Parallelism

```bash
python -m sglang.launch_server \
  --model-path gs://my-bucket/models/llama-70b/ \
  --tp 4 \
  --model-loader-extra-config '{"distributed": true}'
```

## Configuration

### Load Format

The `runai_streamer` load format is designed for object storage, SSDs, and shared filesystems.

```bash
python -m sglang.launch_server \
  --model-path s3://bucket/model/ \
  --load-format runai_streamer
```

### Extended Configuration Parameters

Use `--model-loader-extra-config` to pass additional configuration as a JSON string:

```bash
python -m sglang.launch_server \
  --model-path s3://bucket/model/ \
  --model-loader-extra-config '{
    "distributed": true,
    "concurrency": 8,
    "memory_limit": 2147483648
  }'
```

#### Available Parameters

<table style={{width: "100%", borderCollapse: "collapse", tableLayout: "fixed"}}>
  <colgroup>
    <col style={{width: "22%"}} />
    <col style={{width: "16%"}} />
    <col style={{width: "44%"}} />
    <col style={{width: "18%"}} />
  </colgroup>
  <thead>
    <tr style={{borderBottom: "2px solid #d55816"}}>
      <th style={{textAlign: "left", padding: "10px 12px", fontWeight: 700, whiteSpace: "nowrap", backgroundColor: "rgba(255,255,255,0.02)"}}>Parameter</th>
      <th style={{textAlign: "left", padding: "10px 12px", fontWeight: 700, whiteSpace: "nowrap", backgroundColor: "rgba(255,255,255,0.05)"}}>Type</th>
      <th style={{textAlign: "left", padding: "10px 12px", fontWeight: 700, whiteSpace: "nowrap", backgroundColor: "rgba(255,255,255,0.02)"}}>Description</th>
      <th style={{textAlign: "left", padding: "10px 12px", fontWeight: 700, whiteSpace: "nowrap", backgroundColor: "rgba(255,255,255,0.05)"}}>Default</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td style={{padding: "9px 12px", fontWeight: 500, backgroundColor: "rgba(255,255,255,0.02)"}}><code>distributed</code></td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.05)"}}>bool</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.02)"}}>Enable distributed streaming for multi-GPU setups. Automatically set to <code>true</code> for object storage paths on CUDA-like devices.</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.05)"}}>Auto-detected</td>
    </tr>
    <tr>
      <td style={{padding: "9px 12px", fontWeight: 500, backgroundColor: "rgba(255,255,255,0.02)"}}><code>concurrency</code></td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.05)"}}>int</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.02)"}}>Number of concurrent download streams. Higher values can improve throughput for large models.</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.05)"}}>4</td>
    </tr>
    <tr>
      <td style={{padding: "9px 12px", fontWeight: 500, backgroundColor: "rgba(255,255,255,0.02)"}}><code>memory_limit</code></td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.05)"}}>int</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.02)"}}>Memory limit (in bytes) for the streaming buffer.</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.05)"}}>System-dependent</td>
    </tr>
  </tbody>
</table>

## Performance Considerations

### Distributed Streaming

For multi-GPU setups, enable distributed streaming to parallelize weight loading across processes:

```bash
python -m sglang.launch_server \
  --model-path s3://bucket/model/ \
  --tp 8 \
  --model-loader-extra-config '{"distributed": true}'
```

## Limitations

- **Supported formats**: Only the `.safetensors` weight format is supported.
- **Supported devices**: Distributed streaming is supported on CUDA-like devices; otherwise it falls back to non-distributed streaming.

## See Also

- [Runai model streamer documentation](https://github.com/run-ai/runai-model-streamer)
