sglang/docs_new/docs/sglang-diffusion/cache-dit.mdx

---
title: "Cache-DiT Acceleration"
description: "Configure Cache-DiT acceleration for diffusion inference."
---

SGLang integrates [Cache-DiT](https://github.com/vipshop/cache-dit), a caching acceleration engine for Diffusion Transformers (DiT), to achieve up to **1.69x inference speedup** with minimal quality loss.

## Overview

**Cache-DiT** uses intelligent caching strategies to skip redundant computation in the denoising loop:

- **DBCache (Dual Block Cache)**: Dynamically decides when to cache transformer blocks based on residual differences
- **TaylorSeer**: Uses Taylor expansion for calibration to optimize caching decisions
- **SCM (Step Computation Masking)**: Step-level caching control for additional speedup

## Basic Usage

Enable Cache-DiT by exporting the environment variable and using `sglang generate` or `sglang serve` :

```bash
SGLANG_CACHE_DIT_ENABLED=true \
sglang generate --model-path Qwen/Qwen-Image \
    --prompt "A beautiful sunset over the mountains"
```

## Diffusers Backend

Cache-DiT supports loading acceleration configs from a custom YAML file. For
diffusers pipelines (`diffusers` backend), pass the YAML/JSON path via `--cache-dit-config`. This
flow requires cache-dit >= 1.2.0 (`cache_dit.load_configs`).

### Single GPU inference

Define a `cache.yaml` file that contains:

```yaml
cache_config:
  max_warmup_steps: 8
  warmup_interval: 2
  max_cached_steps: -1
  max_continuous_cached_steps: 2
  Fn_compute_blocks: 1
  Bn_compute_blocks: 0
  residual_diff_threshold: 0.12
  enable_taylorseer: true
  taylorseer_order: 1
```

Then apply the config with:

```bash
sglang generate \
  --backend diffusers \
  --model-path Qwen/Qwen-Image \
  --cache-dit-config cache.yaml \
  --prompt "A beautiful sunset over the mountains"
```

### Distributed inference

- 1D Parallelism

Define a parallelism only config yaml `parallel.yaml` file that contains:

```yaml
parallelism_config:
  ulysses_size: auto
  parallel_kwargs:
    attention_backend: native
    extra_parallel_modules: ["text_encoder", "vae"]
```

Then, apply the distributed inference acceleration config from yaml. `ulysses_size: auto` means that cache-dit will auto detect the `world_size` as the ulysses_size. Otherwise, you should manually set it as specific int number, e.g, 4.

Then apply the distributed config with: (Note: please add `--num-gpus N` to specify the number of gpus for distributed inference)

```bash
sglang generate \
  --backend diffusers \
  --num-gpus 4 \
  --model-path Qwen/Qwen-Image \
  --cache-dit-config parallel.yaml \
  --prompt "A futuristic cityscape at sunset"
```

- 2D Parallelism

You can also define a 2D parallelism config yaml `parallel_2d.yaml` file that contains:

```yaml
parallelism_config:
  ulysses_size: auto
  tp_size: 2
  parallel_kwargs:
    attention_backend: native
    extra_parallel_modules: ["text_encoder", "vae"]
```
Then, apply the 2D parallelism config from yaml. Here `tp_size: 2` means using tensor parallelism with size 2. The `ulysses_size: auto` means that cache-dit will auto detect the `world_size // tp_size` as the ulysses_size.

- 3D Parallelism

You can also define a 3D parallelism config yaml `parallel_3d.yaml` file that contains:

```yaml
parallelism_config:
  ulysses_size: 2
  ring_size: 2
  tp_size: 2
  parallel_kwargs:
    attention_backend: native
    extra_parallel_modules: ["text_encoder", "vae"]
```
Then, apply the 3D parallelism config from yaml. Here `ulysses_size: 2`, `ring_size: 2`, `tp_size: 2` means using ulysses parallelism with size 2, ring parallelism with size 2 and tensor parallelism with size 2.

### Hybrid Cache and Parallelism

Define a hybrid cache and parallel acceleration config yaml `hybrid.yaml` file that contains:

```yaml
cache_config:
  max_warmup_steps: 8
  warmup_interval: 2
  max_cached_steps: -1
  max_continuous_cached_steps: 2
  Fn_compute_blocks: 1
  Bn_compute_blocks: 0
  residual_diff_threshold: 0.12
  enable_taylorseer: true
  taylorseer_order: 1
parallelism_config:
  ulysses_size: auto
  parallel_kwargs:
    attention_backend: native
    extra_parallel_modules: ["text_encoder", "vae"]
```

Then, apply the hybrid cache and parallel acceleration config from yaml.

```bash
sglang generate \
  --backend diffusers \
  --num-gpus 4 \
  --model-path Qwen/Qwen-Image \
  --cache-dit-config hybrid.yaml \
  --prompt "A beautiful sunset over the mountains"
```

## Advanced Configuration

### DBCache Parameters

DBCache controls block-level caching behavior:

<table style={{width: "100%", borderCollapse: "collapse", tableLayout: "fixed"}}>
  <colgroup>
    <col style={{width: "12%"}} />
    <col style={{width: "34%"}} />
    <col style={{width: "14%"}} />
    <col style={{width: "40%"}} />
  </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)"}}>Env Variable</th>
      <th style={{textAlign: "left", padding: "10px 12px", fontWeight: 700, whiteSpace: "nowrap", backgroundColor: "rgba(255,255,255,0.02)"}}>Default</th>
      <th style={{textAlign: "left", padding: "10px 12px", fontWeight: 700, whiteSpace: "nowrap", backgroundColor: "rgba(255,255,255,0.05)"}}>Description</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td style={{padding: "9px 12px", fontWeight: 500, backgroundColor: "rgba(255,255,255,0.02)"}}>Fn</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.05)"}}>`SGLANG_CACHE_DIT_FN`</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.02)"}}>1</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.05)"}}>Number of first blocks to always compute</td>
    </tr>
    <tr>
      <td style={{padding: "9px 12px", fontWeight: 500, backgroundColor: "rgba(255,255,255,0.02)"}}>Bn</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.05)"}}>`SGLANG_CACHE_DIT_BN`</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.02)"}}>0</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.05)"}}>Number of last blocks to always compute</td>
    </tr>
    <tr>
      <td style={{padding: "9px 12px", fontWeight: 500, backgroundColor: "rgba(255,255,255,0.02)"}}>W</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.05)"}}>`SGLANG_CACHE_DIT_WARMUP`</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.02)"}}>4</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.05)"}}>Warmup steps before caching starts</td>
    </tr>
    <tr>
      <td style={{padding: "9px 12px", fontWeight: 500, backgroundColor: "rgba(255,255,255,0.02)"}}>R</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.05)"}}>`SGLANG_CACHE_DIT_RDT`</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.02)"}}>0.24</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.05)"}}>Residual difference threshold</td>
    </tr>
    <tr>
      <td style={{padding: "9px 12px", fontWeight: 500, backgroundColor: "rgba(255,255,255,0.02)"}}>MC</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.05)"}}>`SGLANG_CACHE_DIT_MC`</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.02)"}}>3</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.05)"}}>Maximum continuous cached steps</td>
    </tr>
  </tbody>
</table>

### TaylorSeer Configuration

TaylorSeer improves caching accuracy using Taylor expansion:

<table style={{width: "100%", borderCollapse: "collapse", tableLayout: "fixed"}}>
  <colgroup>
    <col style={{width: "12%"}} />
    <col style={{width: "36%"}} />
    <col style={{width: "14%"}} />
    <col style={{width: "38%"}} />
  </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)"}}>Env Variable</th>
      <th style={{textAlign: "left", padding: "10px 12px", fontWeight: 700, whiteSpace: "nowrap", backgroundColor: "rgba(255,255,255,0.02)"}}>Default</th>
      <th style={{textAlign: "left", padding: "10px 12px", fontWeight: 700, whiteSpace: "nowrap", backgroundColor: "rgba(255,255,255,0.05)"}}>Description</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td style={{padding: "9px 12px", fontWeight: 500, backgroundColor: "rgba(255,255,255,0.02)"}}>Enable</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.05)"}}>`SGLANG_CACHE_DIT_TAYLORSEER`</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.02)"}}>false</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.05)"}}>Enable TaylorSeer calibrator</td>
    </tr>
    <tr>
      <td style={{padding: "9px 12px", fontWeight: 500, backgroundColor: "rgba(255,255,255,0.02)"}}>Order</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.05)"}}>`SGLANG_CACHE_DIT_TS_ORDER`</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.02)"}}>1</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.05)"}}>Taylor expansion order (1 or 2)</td>
    </tr>
  </tbody>
</table>

### Combined Configuration Example

DBCache and TaylorSeer are complementary strategies that work together, you can configure both sets of parameters
simultaneously:

```bash
SGLANG_CACHE_DIT_ENABLED=true \
SGLANG_CACHE_DIT_FN=2 \
SGLANG_CACHE_DIT_BN=1 \
SGLANG_CACHE_DIT_WARMUP=4 \
SGLANG_CACHE_DIT_RDT=0.4 \
SGLANG_CACHE_DIT_MC=4 \
SGLANG_CACHE_DIT_TAYLORSEER=true \
SGLANG_CACHE_DIT_TS_ORDER=2 \
sglang generate --model-path black-forest-labs/FLUX.1-dev \
    --prompt "A curious raccoon in a forest"
```

### SCM (Step Computation Masking)

SCM provides step-level caching control for additional speedup. It decides which denoising steps to compute fully and
which to use cached results.

**SCM Presets**

SCM is configured with presets:

<table style={{width: "100%", borderCollapse: "collapse", tableLayout: "fixed"}}>
  <colgroup>
    <col style={{width: "18%"}} />
    <col style={{width: "22%"}} />
    <col style={{width: "22%"}} />
    <col style={{width: "38%"}} />
  </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)"}}>Preset</th>
      <th style={{textAlign: "left", padding: "10px 12px", fontWeight: 700, whiteSpace: "nowrap", backgroundColor: "rgba(255,255,255,0.05)"}}>Compute Ratio</th>
      <th style={{textAlign: "left", padding: "10px 12px", fontWeight: 700, whiteSpace: "nowrap", backgroundColor: "rgba(255,255,255,0.02)"}}>Speed</th>
      <th style={{textAlign: "left", padding: "10px 12px", fontWeight: 700, whiteSpace: "nowrap", backgroundColor: "rgba(255,255,255,0.05)"}}>Quality</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td style={{padding: "9px 12px", fontWeight: 500, backgroundColor: "rgba(255,255,255,0.02)"}}>`none`</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.05)"}}>100%</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.02)"}}>Baseline</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.05)"}}>Best</td>
    </tr>
    <tr>
      <td style={{padding: "9px 12px", fontWeight: 500, backgroundColor: "rgba(255,255,255,0.02)"}}>`slow`</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.05)"}}>~75%</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.02)"}}>~1.3x</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.05)"}}>High</td>
    </tr>
    <tr>
      <td style={{padding: "9px 12px", fontWeight: 500, backgroundColor: "rgba(255,255,255,0.02)"}}>`medium`</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.05)"}}>~50%</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.02)"}}>~2x</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.05)"}}>Good</td>
    </tr>
    <tr>
      <td style={{padding: "9px 12px", fontWeight: 500, backgroundColor: "rgba(255,255,255,0.02)"}}>`fast`</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.05)"}}>~35%</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.02)"}}>~3x</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.05)"}}>Acceptable</td>
    </tr>
    <tr>
      <td style={{padding: "9px 12px", fontWeight: 500, backgroundColor: "rgba(255,255,255,0.02)"}}>`ultra`</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.05)"}}>~25%</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.02)"}}>~4x</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.05)"}}>Lower</td>
    </tr>
  </tbody>
</table>

**Usage**

```bash
SGLANG_CACHE_DIT_ENABLED=true \
SGLANG_CACHE_DIT_SCM_PRESET=medium \
sglang generate --model-path Qwen/Qwen-Image \
    --prompt "A futuristic cityscape at sunset"
```

**Custom SCM Bins**

For fine-grained control over which steps to compute vs cache:

```bash
SGLANG_CACHE_DIT_ENABLED=true \
SGLANG_CACHE_DIT_SCM_COMPUTE_BINS="8,3,3,2,2" \
SGLANG_CACHE_DIT_SCM_CACHE_BINS="1,2,2,2,3" \
sglang generate --model-path Qwen/Qwen-Image \
    --prompt "A futuristic cityscape at sunset"
```

**SCM Policy**

<table style={{width: "100%", borderCollapse: "collapse", tableLayout: "fixed"}}>
  <colgroup>
    <col style={{width: "16%"}} />
    <col style={{width: "42%"}} />
    <col style={{width: "42%"}} />
  </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)"}}>Policy</th>
      <th style={{textAlign: "left", padding: "10px 12px", fontWeight: 700, whiteSpace: "nowrap", backgroundColor: "rgba(255,255,255,0.05)"}}>Env Variable</th>
      <th style={{textAlign: "left", padding: "10px 12px", fontWeight: 700, whiteSpace: "nowrap", backgroundColor: "rgba(255,255,255,0.02)"}}>Description</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td style={{padding: "9px 12px", fontWeight: 500, backgroundColor: "rgba(255,255,255,0.02)"}}>`dynamic`</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.05)"}}>`SGLANG_CACHE_DIT_SCM_POLICY=dynamic`</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.02)"}}>Adaptive caching based on content (default)</td>
    </tr>
    <tr>
      <td style={{padding: "9px 12px", fontWeight: 500, backgroundColor: "rgba(255,255,255,0.02)"}}>`static`</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.05)"}}>`SGLANG_CACHE_DIT_SCM_POLICY=static`</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.02)"}}>Fixed caching pattern</td>
    </tr>
  </tbody>
</table>

## Environment Variables

All Cache-DiT parameters can be configured via environment variables.
See [Environment variables](./environment-variables) for the complete list.

## Supported Models

SGLang Diffusion x Cache-DiT supports almost all models originally supported in SGLang Diffusion:

<table style={{width: "100%", borderCollapse: "collapse", tableLayout: "fixed"}}>
  <colgroup>
    <col style={{width: "30%"}} />
    <col style={{width: "70%"}} />
  </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)"}}>Model Family</th>
      <th style={{textAlign: "left", padding: "10px 12px", fontWeight: 700, whiteSpace: "nowrap", backgroundColor: "rgba(255,255,255,0.05)"}}>Example Models</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td style={{padding: "9px 12px", fontWeight: 500, backgroundColor: "rgba(255,255,255,0.02)"}}>Wan</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.05)"}}>Wan2.1, Wan2.2</td>
    </tr>
    <tr>
      <td style={{padding: "9px 12px", fontWeight: 500, backgroundColor: "rgba(255,255,255,0.02)"}}>Flux</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.05)"}}>FLUX.1-dev, FLUX.2-dev</td>
    </tr>
    <tr>
      <td style={{padding: "9px 12px", fontWeight: 500, backgroundColor: "rgba(255,255,255,0.02)"}}>Z-Image</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.05)"}}>Z-Image-Turbo</td>
    </tr>
    <tr>
      <td style={{padding: "9px 12px", fontWeight: 500, backgroundColor: "rgba(255,255,255,0.02)"}}>Qwen</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.05)"}}>Qwen-Image, Qwen-Image-Edit</td>
    </tr>
    <tr>
      <td style={{padding: "9px 12px", fontWeight: 500, backgroundColor: "rgba(255,255,255,0.02)"}}>Hunyuan</td>
      <td style={{padding: "9px 12px", backgroundColor: "rgba(255,255,255,0.05)"}}>HunyuanVideo</td>
    </tr>
  </tbody>
</table>

## Performance Tips

1. **Start with defaults**: The default parameters work well for most models
2. **Use TaylorSeer**: It typically improves both speed and quality
3. **Tune R threshold**: Lower values = better quality, higher values = faster
4. **SCM for extra speed**: Use `medium` preset for good speed/quality balance
5. **Warmup matters**: Higher warmup = more stable caching decisions

## Limitations

- **SGLang-native pipelines**: Distributed support (TP/SP) is not yet validated; Cache-DiT will be automatically
  disabled when `world_size > 1`.
- **SCM minimum steps**: SCM requires >= 8 inference steps to be effective
- **Model support**: Only models registered in Cache-DiT's BlockAdapterRegister are supported

## Troubleshooting

### SCM disabled for low step count

For models with < 8 inference steps (e.g., DMD distilled models), SCM will be automatically disabled. DBCache
acceleration still works.

## References

- [Cache-DiT](https://github.com/vipshop/cache-dit)
- [SGLang diffusion](../../sglang-diffusion/intro)